The MCS6501, a first and very rare member of the MOS Technology 65xx CPU family.
Introduced in 1975 with the MCS6502 to MCS6505, pin compatible with the Motorola 6800 and, after legal issues, not produced afterwards.
An advert in the magazine Electronics August 1975, the price is incredible low for these days at $20.

The (preliminary) datasheet of August 1975 is the only document where the 6501 is documented. PDF format, Below the pages are shown.

More photos found on the web, the 6501 is at least produced in week 34 to week 50 of 1975.

Afaik the only known system where the 6501 was used is the The Digital Group 6501 CPU board.

The 6500 Hardware manual from 1976 time had detailed information on 6501, see page 30 – 40.

The following table summarizes what makes the 6501 pin compatible with the 6800. Note the two phase non-inverting clock, Data Bus Enable

Pinout differences
Pin 6800 6501 6502
2 Halt Ready Ready
3 ∅1 (in) ∅1 (in) ∅1 (out)
5 Valid Memory Address (output) Valid Memory Address (output, always high) N.C.
7 Bus Available (output) Bus Available (output) SYNC
36 Data Bus Enable (input) Data Bus Enable (input) N.C.
37 ∅2 (in) ∅2 (in) ∅0 (in)
38 N.C. N.C. Set Overflow Flag
39 Three-State Control N.C. ∅2 (out)

From the 1976 Hardware manual page 30-40


6530 TIM IC

New in my collection: a TIM IC! 6530-004 2577


New commands for TIM

An article from Micro February 1979 shows how to enhance the TIM monitor.



With the name SUPERKIM an engineer called Paul Lamar designed a SBC around the 6502.
The main design decisions were to be a superset of the KIM-1, requiring no alteration of KIM-1 programs or user interface (the keyboard/display!) but with much more extendable resources. And the result is just right, it Is a KIM-1 with many improvements!
I have never seen this system in real life here in the Netherlands, only advertisements in the then current, dedicated to the 6502, magazines.

The heart of the system is the 6502 at 1 MHz and the well-known KIM-1 RRIOT’s 6530-002 and 6530-003,  the six  seven segment led  displays, a keyboard equivalent tot the KIM-1, the cassette interface and RS-232-C serial interface.  Extra are 4kRAM (from 1K on the KIM-1), 4×6522 VIA’s, 8K EPROM , all socketed and not populated by default. A 8 bit priority encoded IRQ and space for wire wrapping on the board. Also included are fully decoded address map lines, tri-state buffers for address and data bus on wire wrap headers and a power supply for 12V, 1A input ging 5V and 12V.

The KIM-1 ’emulation’  is complete, since the KIM-1 6530’s are there, at the default location and relevant KIM-1 hardware like seven segment display and keyboard, audio cassette interface and tty interface and edge connector.

The SUPERKIMwas sold by Microproducts as shown in this advertisement page in the magazine Micro, issue 13 June 1979:

Paul Lamar initially developed Road Test Systems with the KIM-1 and the limitations in resources made him develop the SUPERKIM.

Articles describing the use of the SUPERKIM in robots and Road Test systems:

IEEE: Microprocessor based System for roll-down and acceleration tests. LA-UR 78-3234 D.K. Lynn, C. Derouin and P. Lamar

Articles about the Computerized Road Test System from Lamar Instruments

From the blog of Dennis Simanaitis:


I came upon some photos summarizing automotive testing as practiced when I arrived at R&T in the late 1970s. One photo brought back memories of the excitement, the technical expertise, the glamor.
Weighing a test car, c. 1979.
We weighed our test cars at a local builders supply. The idea of having our own scales capable of obtaining individual corner weights was far off in a digital future. Rough and ready though the scene appeared, the supply-yard scales were California-certified and nearby.
Track testing took place at Orange County International Raceway, a local drag strip with abbreviated road course. A fabled place: Bob Bondurant used it for his first driving school, opened in February 1968. The second week, Bob had two students: actors Paul Newman and Robert Wagner, both preparing for the movie Winning. P.L. Newman continued, racing and winning.
In 1977, R&T’s John Dinkel, my predecessor as engineering editor, asked a fellow named Paul Lamar whether any new computerized gizmos might be employed in gathering acceleration and braking data.

John Dinkel, at the wheel, and Paul Lamar examine computerized data. (That’s their story; and they’re sticking to it.) This and other images from R&T, May 1977.

Paul is a cool guy. Beginning in 1966, he worked with Texan Jim Hall in developing the Chaparrals 2C, 2D and 2F. (Paul was responsible for most of the body design of the 2F.) After that, he set up his own company doing race car development and equipment design. For a long time, he has been active with aircraft applications of Mazda rotary engines, at a website proudly “Powered by Linux!”

Back in 1977, Paul said to JD (as Dinkel was known), “I recommend you consider a microprocessor. It’s the coming thing in electronics.” Paul followed up on his recommendation with devising the first computerized test equipment used by an auto magazine. Hitherto, acceleration testing was a two-person task, one driving, the other punching an array of stopwatches based on measurements of a bulky 5th-wheel.
Another gizmo, the sainted R&T Tapley Meter used to give impressive data with which we younger readers were highly impressed (“Wow! Off-scale!”), though we never really understood what it was measuring. (It turns out the Tapley Meter was a pendulum-driven accelerometer.)
When I began at R&T in early 1979, Paul’s computerized black box became an everyday part of my track testing. Its heart was an MOS Technology MCS 6502 Microprocessor Array.
The “sixty-five-oh-two” was pivotal in the computer industry: Its price was one-sixth that of comparable products and brought about a rapid decrease in competitors’ pricing and a dramatic increase in microprocessor availability. In retrospect, it likely had the computing power of a toy digital clock operated by a potato battery, but at the time it was state-of-the-art.
The Lamar black box had a keyboard for programming. (How’s your base-16? Mine is sketchy at best.)
The Lamar black box’s keyboard was one of its ways for entering a program—in hexadecimal (base-16) code! Fortunately, once debugged, the acceleration and braking programs were stored on a separate Sony
cassette tape recorder and played back into the 6502 when changing from one test to the other.
Alas, the black box had insufficient memory to store them. Also, reprogramming turned out to be occasionally heat-sensitive: I would do the acceleration testing, say, then turn on the car’s a/c to cool off the interior for a bit. Only then would the Sony convey its bops and beeps successfully to the black box.
The 6502’s liquid crystal displays gave information on time, car speed and distance traveled. The Sony cassette tape recorder to its right swapped the 6502’s programs.
Sensitive though it could be, the setup was more accurate than stopwatch-punching and it was a one-person operation. Results were printed on a strip of paper by a separate device, a modified Addo desk calculator residing on the passenger seat. (Paul’s second-gen black box had a built-in printer and enough memory to eliminate the pesky reprogramming.)
Typical results from a separate printer, a modified Addo desk calculator.
The Lamar 5th-wheel was decidedly easier to use than its traditional counterpart. It weighed 20 lbs. versus the clunky one’s 40 lbs. and attached with bungee cords, not potentially bumper-damaging clamps.
The Lamar 5th-wheel compared favorably with its traditional counterpart. It could also be disassembled for shipping.
In 1986, I documented our testing procedures in a presentation to the Society of Automotive Engineers, SAE Paper 861114, “A Magazine’s View on Automotive Testing.” The paper was accompanied by a short film completely produced by R&T, a story in itself. This was back before video cameras—and ages before smart phone imaging.
R&T’s Cecil B. “Joe” DeRusz shot the flick using an Arri Arriflex 16-mm camera, the best of its kind, rented from a Hollywood outlet. We had a vague shooting script based on the technical details of the SAE Paper. But I have vivid memories of Rusz figuring out angles, the entries into frame and exits out of it. I recall we produced the film in a few days of on-again/off-again shooting. Likely over budget. There were lunches after all.


In a two part article in the magazine Robotis Age 1980-1981, Don McaAllister describes the interfacing an programming of the SUPERKIM for the control of the Lour Control ET-2 robot shell.

Tangerine Microtan 65

Have a look here for full information, including new PCB’s and software on the famous Tangerine Microtan 65 system.




Two IC’s 65C102 added to the IC collection.

Rockwell, 8639 and 9009 date codes.


6504 6507 65c802 IC photos added

I got hold of a rare 65c802 and some NOS 6504 and 6507’s.

In the 65XX IC gallery now photos!

6502 Microprocessor Kit

Design and text by Wichit Sirichote. Full text and files at his website here. The kit is available for sale, kit or assembled!

Wichit picked the 65C02 CPU and designed the microcomputer kit with HEX keys and 7-segment LED displays, wrote the monitor program using 6502 instructions. with the TASM assembler. The circuit is simple and easy build.

Hardware specification:

1. CPU: 65SC02, CMOS 8-bit @1MHz clock (a G65SC02 in my kit)
2. Memory: 32kB RAM, 16kB EPROM
3. Decoder chip: GAL16V8 PLD
4. Display: 6-digit 7-segment LED
5 . Keyboard: 36 keys
6 . RS232 port: 2400 bit/s
7 . Debugging LED: 8-bit GPIO1 LED
8 . SystemTick: 10ms tick
9. Text LCD interface: direct CPU bus interface text LCD
10. Expansion header: 40-pin header

Software descriptions: The monitor program was written in 6502 assembly. The source code was translated to hex code using TASM assembler. Main body is a forever loop scanning keyboard and 7-segment display. When a key is pressed the associated functions will be serviced. Details are explained as the comments in the source code.

The monitor program features are:

1.Memory contents can be edited directly with hex keys.
2. User registers for program testing
3. Single instruction execution, no need for jumpers.
4. Relative byte calculation,
5. Download hex file,
6. Zero page display.
7. Inspection of registers, processor status flags and more.

All sources are supplied, with TASM assembler syntax.
The kit I have is running monitor version 1, the current monitor of 2021 is version 4. Easy to burn into the EPROM or you can load it into RAM for debugging/testing a new version.

6502 kit User Manual 2015
6502 kit User Manual V2 June 2021
Build your own 6502 Microprocessor Kit
Programming manual
Monitor V4 4 listing
Microchess on the 6502 kit manual
Microchess on the 6502 kit archive
6502 kit circuit diagram
TICK source
PLD source
Assembler fragments for the kit and TASM older version, see the next archive
TASM 32 bit, runs on 64 bit Windows as console application
Assembler fragment for 7 segment access
Source monitor V1
Source monitor V4 2021

Serial I/O

The monitor has routines for bit banged serial I/O (at RS232C levels) at 2400 baud. The monitor offers Intel Hex and MOS papertape format up/download. This makes it easy to cross develop software, edit and assemble, the download the object on a Tera term terminal session for example.
The serial routines are bit banged, the output line is shared with the little speaker. This means there is quite some noise from the speaker when serial output is done, and when the speaker is activated  (e.g. when you press Reset) the serial output shows annoying trash, as you can see in the following screenshot.

You also see in the screenshot it can be used to run terminal based programs on the serial I/O. Once the program is limited to serial I/O it is fine.
Porting KIM-1 programs mean there is no hardware echo problem, so you have to do the echo yourself. Also serial I/O uses zeropage (RED_D, REG_E)  $80 and $81. That may mean you have to use your own serial I/O routines, copied from the monitor but using more appropriate zeropage addresses,

How to use the serial I/O.

Note that zeropage is on the kit free from 0 to $7F!

The routines in the 6502 microprocessor kit use all registers during the bit banging output.
So it is important to save them before and restore afterwards. The following code fragments (used in the second screenshot, part of the CPU test routines in the KIm-1 Simulator achieve that.

THe 6502 microprocessor has a connector for LCD displays. Example source is included.

ysave = $00  ; zeropage, choose appropriate location!
xsave = $01
asave = $03
; 6502 kit character I/O
XGETCH = $C054 ; GETCH (serial)
XOUTCH = $C01E ; OUTCH (serial)

 STA asave 
 STY ysave
 STX xsave
 LDY ysave
 LDX xsave
 LDA asave

 STY ysave
 STX xsave
 LDY ysave
 LDX xsave

; 6502 CPU board test program serial
; 6502 kit monitor
pstring = $C08E
outch = $C01E
inch  = $C054
crlf  = $C09D
CR      = $0d           ; Carriage return
        .org $0200
        jsr pstring     ; print version
        jsr crlf
        lda #'>'        ; display prompt
        jsr outch
        jsr inch        ; read from serial in
        cmp #CR         ; end of line?
        beq pr
        jsr outch
        jmp loopch         ; loop 

Example programs for serial I/O

0001 0000 ; This program looks at ways to determine which type of 6502-series
0002 0000 ; processor you are using. This version runs on the PAL-1 (a KIM clone).
0003 0000 ;
0004 0000 ; By Jim McClanahan, W4JBM, January 2021
0005 0000 ; adapted to 6502 kit Hans Otten, January 2022
0006 0000 ;
0007 0000 ; Build with:
0008 0000 ; $ tasm -65 <filename>.asm
0009 0000 ;
0010 0000 ;
0011 0000
0012 0000 ;
0013 0000 ; For whatever system we use, we need two routines defined:
0014 0000 ;
0015 0000 ; *** 6502 kit routine ***
0016 0000 ;
0017 0000 ; A routine to send a byte to the console...
0018 0000 outch = $C01E ; Send one byte to the output port (OUTCH)
0019 0000
0020 0000 ; Define any constants we want to use...
0021 0000 CR = $0D
0022 0000 LF = $0A
0023 0000
0024 0000 ; Location isn't particularly important...
0025 0200 .org $0200
0026 0200
0027 0200 ; Set up the stack
0028 0200 ;
0029 0200 ; This is not needed if called from a monitor
0030 0200 ;STACK: LDX #$FF
0031 0200 ; TXS
0032 0200 ;
0033 0200 ; clear kit junk
0034 0200 ;
0035 0200 A9 0D lda #CR
0036 0202 20 1E C0 jsr outch ;
0037 0205 A9 0A lda #LF
0038 0207 20 1E C0 jsr outch
0039 020A
0040 020A ; First, let's see what happens to the Zero flag in
0041 020A ; the decimal mode
0042 020A F8 TEST1: SED ; Set Decimal (BCD) Mode
0043 020B 18 CLC ; Clear the Carry Flag
0044 020C A9 99 LDA #$99 ; Load a BCD 99 (which is also $99)
0045 020E 69 01 ADC #$01 ; ...and add 1
0046 0210 08 PHP ; Push processor status byte to stack
0047 0211 8D 75 02 STA TSTR1 ; Store the result in memory
0048 0214 D8 CLD ; Because we don't want to forget
0049 0215
0050 0215 ; At this point, the Acc is $00 but the original 6502 did not
0051 0215 ; set the Zero flag when this happened in the decimal mode
0052 0215 ; while the later R6502 and 65C02 did.
0053 0215
0054 0215 F0 10 BEQ TEST1B
0055 0217 A9 79 TEST1A: LDA #MSG1 & 255 ; Point to Message 1
0056 0219 8D 6A 02 STA PRINT+1
0057 021C A9 02 LDA #MSG1 / 256
0058 021E 8D 6B 02 STA PRINT+2
0059 0221 20 67 02 JSR SHWMSG ; Display result (no Z flag)
0060 0224 4C 34 02 JMP TEST2
0061 0227
0062 0227 A9 A1 TEST1B: LDA #MSG2&255 ; Point to Message 2
0063 0229 8D 6A 02 STA PRINT+1
0064 022C A9 02 LDA #MSG2/256
0065 022E 8D 6B 02 STA PRINT+2
0066 0231 20 67 02 JSR SHWMSG ; Display result (Z flag set)
0067 0234
0068 0234 ; On the original 6502, undefined instructions could do various
0069 0234 ; (and sometimes seemingly unpredictable) things. On later versions,
0070 0234 ; some of the unused instructions were pressed into use while others
0071 0234 ; were changed to be a "safe" NOP (no operation).
0072 0234 ;
0073 0234 ; $EA is NOP and on the original most of the $xA instructions also
0074 0234 ; act as NOPs. $1A is one that seems to be a well-behaved NOP, but
0075 0234 ; the R6502 and 65C02 used that previously undefined code to
0076 0234 ; implement an INC A instruction.
0077 0234 ;
0078 0234 ; The following code checks to see what $3A does...
0079 0234
0080 0234 68 TEST2: PLA ; Before the test, let's story the processor
0081 0235 8D 76 02 STA TSTR2 ; results from the last test.
0082 0238 A9 FF LDA #$FF ; Load the accumulator
0083 023A 1A .BYTE $1A ; Either a NOP or INA (similar to INX and INY)
0084 023B 49 00 EOR #$0 ; Let's make sure the flags are set
0085 023D 08 PHP ; Save the processor status register
0086 023E 8D 77 02 STA TSTR3 ; Store result in memory
0087 0241 F0 10 BEQ TEST2B ; Does A == 0?
0088 0243 A9 C0 TEST2A: LDA #MSG3&255 ; If not, Point to Message 3
0089 0245 8D 6A 02 STA PRINT+1
0090 0248 A9 02 LDA #MSG3/256
0091 024A 8D 6B 02 STA PRINT+2
0092 024D 20 67 02 JSR SHWMSG
0093 0250 4C 60 02 JMP FINISH
0094 0253
0095 0253 A9 E1 TEST2B: LDA #MSG4&255 ; Point to Message 4
0096 0255 8D 6A 02 STA PRINT+1
0097 0258 A9 02 LDA #MSG4/256
0098 025A 8D 6B 02 STA PRINT+2
0099 025D 20 67 02 JSR SHWMSG
0100 0260
0101 0260 68 FINISH: PLA ; Let's store the processor status
0102 0261 8D 78 02 STA TSTR4 ; from the last test.
0103 0264 loop
0104 0264 4C 64 02 JMP loop ; We're done so jump back to the monitor
0105 0267 ; RTS ; ...depending on the system, RTS may work
0106 0267
0107 0267 ; If you don't want to go to the monitor, you can loop instead...
0108 0267
0109 0267 ;LOOP: JMP LOOP ; Now just loop endlessly...
0110 0267
0111 0267 ; Display a null-terminated message...
0112 0267
0113 0267 A2 00 SHWMSG: LDX #$0 ; Show Message Subroutine
0114 0269 BD 79 02 PRINT: LDA MSG1,X ; SELF MODIFYING Address and Offset
0115 026C F0 06 BEQ DONE ; Did we just load a $00 end-of-string?
0116 026E 20 1E C0 JSR outch ; If not, print it
0117 0271 E8 INX ; Point to next character
0118 0272 D0 F5 BNE PRINT ; Branch to do it again...
0119 0274 60 DONE: RTS ; Jump here at end-of-string or 256 characters
0120 0275
0121 0275 ;
0122 0275 ; If we don't have console output, you can get information on
0123 0275 ; what happened by looking at the results stored here.
0124 0275 ;
0125 0275 ; 7 4 3 0
0126 0275 ; ---- ----
0127 0275 ; NVbb DIZC
0128 0275 ;
0129 0275 ; N - Negative
0130 0275 ; V - oVerflow
0131 0275 ; D - Decimal mode
0132 0275 ; I - Interrupt disable
0133 0275 ; Z - Zero
0134 0275 ; C - Carry
0135 0275 ;
0136 0275 ; bb should be %11 (usually a $3x in these tests) to show the
0137 0275 ; status was pushed to the stack using PHP and not the result
0138 0275 ; of an interupt.
0139 0275
0140 0275 55 TSTR1 .BYTE $55 ; Result in Decimal mode of $99 + $01
0141 0276 55 TSTR2 .BYTE $55 ; ...and process status register
0142 0277 55 TSTR3 .BYTE $55 ; Result of $FF and then executing NOP/INC A
0143 0278 55 TSTR4 .BYTE $55 ; ...and the process status register
0144 0279
0145 0279 ; TSTR1, TSTR2, TSTR3, and TSTR4 should be:
0146 0279 ; $00 $39 $FF $B0 for the original 6502
0147 0279 ; $00 $3B $00 $32 for the 65C02
0148 0279
0149 0279 ; Our messages follows...
0150 0279
0151 0279 0D 0A 44 45 MSG1 .byte CR,LF,"DEC Add does not set Z. (Orig 6502)",CR,LF, 0
0151 027D 43 20 41 64
0151 0281 64 20 64 6F
0151 0285 65 73 20 6E
0151 0289 6F 74 20 73
0151 028D 65 74 20 5A
0151 0291 2E 20 28 4F
0151 0295 72 69 67 20
0151 0299 36 35 30 32
0151 029D 29 0D 0A 00
0152 02A1 0D 0A 44 45 MSG2 .byte CR,LF,"DEC Add did set Z. (65C02)",CR,LF, 0
0152 02A5 43 20 41 64
0152 02A9 64 20 64 69
0152 02AD 64 20 73 65
0152 02B1 74 20 5A 2E
0152 02B5 20 28 36 35
0152 02B9 43 30 32 29
0152 02BD 0D 0A 00
0153 02C0 24 31 41 20 MSG3 .byte "$1A acts as a NOP. (Orig 6502)",CR,LF, 0
0153 02C4 61 63 74 73
0153 02C8 20 61 73 20
0153 02CC 61 20 4E 4F
0153 02D0 50 2E 20 28
0153 02D4 4F 72 69 67
0153 02D8 20 36 35 30
0153 02DC 32 29 0D 0A
0153 02E0 00
0154 02E1 24 31 41 20 MSG4 .byte "$1A acts as INC A. (65C02)",CR,LF, 0
0154 02E5 61 63 74 73
0154 02E9 20 61 73 20
0154 02ED 49 4E 43 20
0154 02F1 41 2E 20 28
0154 02F5 36 35 43 30
0154 02F9 32 29 0D 0A
0154 02FD 00
0155 02FE
0156 02FE .END
0157 02FE
tasm: Number of errors = 0

Old micros: SYM-1 6502 mini SBC and more

The website is to look at designs of older microcomputers and provide information to people to be able to build some of these for their own use. It is aimed at micro enthusiast with reasonable knowledge of electronics and digital/microprocessor theory.

There are still many older “original”microcomputer boards for sale  (on Ebay etc) .. but tend to be rather expensive and in most cases those boards are either not functioning (due to age) ..or rather limited in their operation or not being able actually connect them to anything useful  (like current PC’s or terminals).

So in my quest to play around with some of different varieties of microcomputers (like SC/MP, 6800’s, 6502’s,TMS9900’s, 68000 etc) I am sharing some of the design (like pcb’s).. so people can build their own. I do provide some components .. but this is not a commercial venture, so you might have to source other bits from different sources to complete any of the designs. Some are prototype and some are fully built sbc (single board computers).


SYM-1 6502 mini sbc

SYM-1 6502 mini and Maxi SBC

The following article is a local copy of the site of Michael Cvetanovski, all design and ‘me’ in the text below is by and (C)  Michael Cvetanovski.
The copy here is for information and archiving only, the original is the place to go for the latest information. The following text (“I”) is by Michael Cvetanovski.

If you are interested in the PCB’s ask Michael, not me! I do not sell them!

SYM-1 6502 mini SBC
SYM-1 Maxi
SYM-1 Maxi built by Norbert Joppen

SYM-1 6502 mini SBC

Bit of History

Once upon a time .. I had a SYM-1 sbc board that I played around with. Wonderful microcomputer for its era (early 1980’s). Like most people due to non use and lack of interest I give that micro away. Since my recent eagerness to dabble with some of the older micros .. I had a go at trying to rebuild the SYM-1 to a reasonable design so I can use most of the SYM-1 features. Having a 6502 chip and a 6532 peripheral chip, I had most bits to be able to create a minimal system to say run the SYM-1 Supermon 1.1 monitor. Following is a prototype that I got working (must admit after some testing time) which is minimal in design in having basically 5 main chips and TTL-USB adapter for comms to a PC. This project is ongoing where I have also reproduced (to a reasonable degree) an imitation keypad similar to the original one from individual pcb type push button keys. Where possible I used particular IC’s (like GAL’s) to minimise the construction and size of the design.

Prototype Board

It mainly consist of the 6502 chip, 6532 peripheral chip, 2732 EPROM for Monitor, 2K 6116 Ram chip and 24pin Atmel GAL chip to provide some of the decoding and interfacing. Additional things on the board are 14pin 1Mhz crystal and an expansion socket to be able to interface to display/keypad. Flying wires are leads to a TTL to USB converter that connects to USB port of a PC. Monitor code is original version 1.1 that you can get from Memory map is original as per SYM-1 board for the monitor, 6532 chip and 2k RAM from 0000-07FF. Gal chip used is Atmel ATF22V10CQ/CQZ. No particular reason for this one .. but you can easily get them from RS components and not that expensive. I will provide the .pld and .jed file for the code to program these. See notes later on.

Prototype board was constructed using a vero type board with a bank of tracks to place the IC’s. Wiring was soldered point to point using wire wrap wire. After initial mounting of the components and testing for shorts etc the board was ready for use. When powered up the board draws about 220mA. See pic below.

Parts for construction

If you are an old micro buff you probably have some if not most parts to construct this mini board. In case you don’t here is few suggestions for major parts.

  • 6502, 6532 you might be lucky enough to get them from China supplies (via Alibaba or Ebay website) prepared to wait 3-4 weeks at least.
  • Atmel pdl (GAL chip) try RS components.. usually very quick delivery. If you cannot program pld’s I can supply the chip programmed.
  • 1Mhz crystal try element14
  • 2732 and 6116 try If you cannot program the 2732 I can supply some Eproms as I have some spares left.
  • TTL to USB adaptor, Many supplies from China via Ebay ..take 3-4 weeks
  • Also look through some forums like this one.

Circuit Design

It basically follows from the original SYM-1 schematics, with simplification of decoding logic with a PLD chip. For minimal system you would need at least a Monitor program, some RAM and an I/O comms. Simplest would be to have RS232 type comms that you can connect to a PC and communicate to the board via terminal type program. So in that case from original design, 6532 chip did the job of communication via pins 16 and 19 to RS232 type interface. Since I was trying to use TTL to USB interface I did not have much success in interfacing the board to the PC. It wasn’t till I actually built an additional keypad to connect to the main board and played around with that I figured out the interface and comms settings. The final comms configuration involved using inverter gates for input and output to serial port (via PLD chip), and the following serial settings on comms port:

  • 4800 Baud
  • no parity
  • 8 bit
  • 1 stop bit
  • handshake none

Original notes and references to RS232 on SYM-1 refer to 3 stop bits .. which confused me initially .. hence it took a while to figure out what works properly.

Schematic and component functions

Following is a schematic of the design. It is using Diptrace software. Note I use point to point schematic (pin ID connections). It does reduce wires ..but for some people it gets bit harder to follow.

Caution: As with any circuit diagrams it is up to you to recheck and make sure it is OK before proceeding to any construction. To best of my ability this is representation of what I have used. I’ve followed other circuit diagrams on the web, only to find some info was wrong. So please check pin outs (especially against datasheets) to make sure all connections are correct. If there is any errors please email me.

Download Schematic

Looking at the schematic here is bit of explanation of some of the component functions:

  • Resistors are basically pullup resistors for inputs to CPU that are not needed.
  • R6 and D1 are just power indicator for the board.
  • S1 (on board pb switch), C5 and R5 are the reset input to 6502. Note also reset is provided from external input via terminal power block.
  • 6532 is wired similar to SYM-1 schematic: A0-A6 for on chip ram addressing. CS1 is A10 and Register Select (RS) is via  PLD chip. R/W is direct from 6502.
  • Chip selects for Rom, Ram and 6532 come from PLD.
  • CRT OUT is inverted to RxData is TxData to CRT IN via PLD inverter gates.
  • PLD provides address decoding and 3 inverter gates. Phi2 and R/W are used to generate RD and WR signals for Rom/Ram.
  • 6116 and 2732 can be any brand as long as the pins are same. Also note which programming voltage is used for the 2732 chip, as they vary greatly.

PLD Function

Atmel PLD is used to provide address decoding and 3 gate inverts for A9 and serial signals. For more info see Atmel website and WinCupl software.

The code for the PLD is shown below:

Name SYM-1;
Partno 0001;
Revision 4k Mon, 2kRam, 6532 Comm;
Date 6/2/15;
Designer mc;
Company mcoz;
Location oz;
Assembly manual;
Device g22v10;

/** Inputs **/
pin [1..6] = [a10..15] ;
pin 7 = phi2;
pin 8 = rnw;
pin 9 = a9;
pin 10 = crtout;
pin 11 = crtin;

/** Outputs **/
pin 19 = !nr;
pin 20 = !nw;
pin 21 = !cs6532;
pin 23 = !csrom;
pin 22 = !csram;
pin 18 = !na9;
pin 16 = !ncrtin;
pin 17 = !ncrtout;

/** Declarations and Intermediate Variable Definitions **/

field ioaddr= [a15..9];
cs6532_eqn = ioaddr:[A4XX..A7XX];
csrom_eqn = (ioaddr:[80XX..8FXX])#(ioaddr:[F0XX..FFXX]) ;
csram_eqn = (ioaddr:[00XX..07XX]) ;

/** Logic Equations **/

nr =phi2&rnw ;
nw = !rnw&phi2 ;
cs6532 = cs6532_eqn ;
csrom = csrom_eqn;
csram = csram_eqn;

The pinout for PLD is as follows:

View pld file

Download jed file

Testing the board

Obviously have the board connected to the PC and use appropriate comms software like Hyperterm (on XP) or RealTerm set to appropriate setting. Also set CAPS ON. (reduces errors). If all OK after pressing the RESET button …press the “Q” key on keyboard . The response should be “.” single dot …where you can give monitor commands after that. Following is snapshot of sample program that is given in Reference manual for SYM-1 that adds two numbers together from memory locations 200 and 201 and places result in 202. You can see that 202 changed from 0 to C6 which is = C1+05.

From this point on you can explore all the monitor commands. Save and Load will not work as provision is not made in this design for saving code to cassette tape. So another way of saving and loading the machine code is via SP an LP (paper tape commands).

Saving and loading code (via terminal)

Refer to paper tape format info in SYM-1 Reference manual (page D-1). So for example to save above code you would issue command

  SP 200-210

and before you press , set terminal program to capture file mode.. which will save text as it is output to the terminal.

Start capture mode and press

the listing should follow.. once character output had stopped ..Stop the capture …

To see what is captured open the captured file with should look like something like this …

Delete the space in first line and replace the “.” in the last line with “;00”. This creates the correct file to upload.

To retrieve the code type in


and send the captured file as text using terminal program ..What you might need to do is delay the character and LF output to about 20ms so the board does not get swamped with incoming characters from the PC serial port. You can adjust the delay to smaller value till the sending of file stops working properly. 20ms+ is usually a safe bet.

Picture above shows loading of the file, listing the code, running it and then listing the result of the addition program. So there you are ..plenty of things to be able to examine ..with minimal system similar to the original SYM-1 board.

I/O via 6532 PIA chip

Ok If you are to use the mini board with RS232 interface only (that is … with NO keypad/display) then the port A (address A400) is free to use for any I/O control. The DDRA (address A401) can be set up for output or input. As a simple example using SYM monitor we can set the DDR to output on all eight PA pins (set DDRA to FF). Then changing the value of I/O Register A (A400 address) from FF to 00 will toggle output on the port A (pins 8-15) from high back to low.

If you want to use the port A as an input then set appropriate bits to 0 in DDRA. Image below shows a crude example of control via Monitor commands. Writing machine/assembly code for more complex task is possible and make the board useful as a micro controller.

Running mini @9600 Baud

It is possible to run the mini board @ 9600. Suggestions have been obtained from 6502 pages website, where following address have been changed:

8AE9 08 --> EA         '   NOP
8AEA 48 --> 60          '  RTS

8AB0 0B -->0A           ' CHANGE NUMBER OF STOP BITS

Changed binary file Supermon 1.1 file for 9600 baud can be downloaded from here. Please note as suggested, once this is changed it might not be possible to run the board at different speeds.

PCB for mini SYM-1

If you are like me I am not best at bread boarding circuits. From the mini board schematic diagram I have generated a pcb design and gerber files that you be able to make your own boards from. See link below.

Word of Caution First
I have not made any of these pcb’s so make sure you check the board out before any component mounting. In case there is any major faults let me know. One mistake that I am aware of is that the polarized caps C5,7 and 8 show the “+” on the wrong side. So make sure you mount polarized caps the correct way around. When I get time will try to correct that.

At this point I am only providing the full set of the gerber files from which you can get the boards manufactured. From more expensive pcb websites the board will work out about $30-$40 .. but if you shop around and get more than one board ..they will probably work out $10-15 each.

Top silk layout and component placement

Most of component placement is self explanatory. It is possible to power the board from TTL/USB connector (by getting +5 volts from PC USB port). But word of caution in doing that. The setup draws about 220mA, so make sure all the connection on J1 are solid. Also if you to use USB power then do not power the board from PWR/RST connector.
Bottom traces…

Top Traces ..


Download set of zipped Gerber files here.

SYM-1 Keyboard

Following is info about keyboard and 6 digit 7 segment display expansion prototype board that was used with mini SYM board to run monitor program from the keypad. It is similar in layout to original SYM-1 board. Keys are made up of pcb push button switches, that have 2 square caps on them. One cap clips over the switch then another CLEAR plastic cap clips over the top again. By placing appropriate size bit of paper with text on it, ANY keyboard key indicator can be made up. (see picture)

The only issue with these switches is that they had too much horizontal (rotational) play and hence keys do not look all lined up. Placing the keys close would eliminate some of that, however mounting the switches on the pcb requires some distance between adjoining pins – so it is not possible to bring the rows close together.

SYM-1 Maxi

This design follows on from the SYM-1 mini board.

  • It improves on previous design by increasing the memory size to possibly full 64K, using NVRam as both RAM and ROM with GAL chip for decoding.
  • 6532 chip is used for comms and general PIO …or possible connection to external keypad (like the original SYM-1 board).
  • There is provision for 2 extra 6522 chips to give extra VIO capabilities to the board.
  • It should be possible to implement the original Monitor software plus any other software like BASIC or the assembler/editor.
  • Communication to the board is via TTL to USB converter and a need for terminal program like REALTerm.

Following is the schematic of the design:

Following is a TOP view of the manufactured PCB ..

And image of assembled board (most of it tested ) …

Current consumption of the board with all chips on board is about 270mA … that is without any external connections to VIA chips ..

There is a slight mod …looking at the above schematic ..pins 18 and 13 have to be swapped ..that is pin18 becomes !a9 and 13 becomes crtout… reason being the the default schematic for the gal chip had pin 13 as i/o pin … but it is only an input pin ..!!!

PLD file to make it all work ….

Name            SYM-1 Maxi;
Partno          0001;
Revision        ver4,monitor,basic,RAE ;
Date           23/11/17;
Designer        mc;
Company         mcoz;
Location        oz;
Assembly        manual;
Device          g22v10;

/** Inputs **/
pin [3..8] = [a15..10] ;
pin 1 = phi2;
pin 2 = rnw;
pin 9 = a9;
pin 10 = a8;
pin 11 = a7;
pin 13 = crtout;
pin 16 = crtin;

/** Outputs **/

pin 14 = !nr;
pin 15 = !nw;
pin 22 = !cs6532;
pin 18 = !na9;
pin 20 = !via2cs;
pin 21 = !via1cs;
pin 23 = !csram;

pin 19 = !ncrtin;
pin 17 = !ncrtout;

/** Declarations and Intermediate Variable Definitions **/

field ioaddr= [a15..7];
cs6532_eqn   = ioaddr:[A4XX..A7XX];  
csrom_eqn   = (ioaddr:[80XX..8FXX])#(ioaddr:[B0XX..FFXX]) ;
csram_eqn   = (ioaddr:[00XX..7FXX]) ;

/** Logic Equations **/

nr = phi2&rnw ;
nw  = !rnw&phi2 ;
cs6532 = cs6532_eqn ;
csrom = csrom_eqn&nr;
csram = csram_eqn#csrom;

You can source all binary files from or try this combined file that has
Monitor imaged @8000-8FFF and F000-FFFF
Basic imaged from C000-DFFF and
RAE imaged @B000-BFFF and E000-EFFF

Download combined binary file

Following is a screen capture of SYM-1 Monitor and SYM BASIC running on maxi Board …

To explore the feature of saving a file to tape cassette do the following …

After typing in “SAVE A” and monitor the output on pin 9 of should be pulsing for a while while the code is being transferred. The rest of circuitry converts the TTL pulses so they can be saved in appropriate audio signals levels for a tape input . Should be able to use any reasonably good tape recorders ..or even modern digital voice recorders ..for saving the code (basic text file) on tape. Similar procedure can be used for saving memory code from Monitor Program via S1 or S2 commands.

RAE for SYM-1

To run the RAE (Resident Assembler Editor) on maxi board ..just type in “G B000” from the monitor prompt .. see image below which shows some test editing and assembling using RAE ..Very Nice …

For more information: see the SYM-1 RAE page.

SYM-1 Maxi build by Norbert Jopppen

After some modifications to the pld file , the cassette interface, the6522’s and the 6532, Basic and RAE are working now. The problems Norbert had were oscillating circuits. Then Norbert found out that the NVRAM is quite critical. On his board a M48Z128Y-120PM1 works well. The Dallas DS1245AB was not reliable.
PLD files by Norbert for the SYM-1 Maxi