0612   1C2A A9 FF               LDA   #$FF       ; COUNT START BIT
0613   1C2C 8D F3 17            STA   CNTH30     ; ZERO CNTH30
0614   1C2F A9 01               LDA   #$01       ; MASK HI ORDER BITS
0615   1C31 2C 40 17    DET1    BIT   SAD        ; TEST 
0616   1C34 D0 19               BNE   START      ; KEYBD SSW TEST
0617   1C36 30 F9               BMI   DET1       ; START BIT TEST
0618   1C38 A9 FC               LDA   #$FC
0619   1C3A 18          DET3    CLC              ; THIS LOOP COUNTS 
0620   1C3B 69 01               ADC   #$01       ; THE START BIT TIME
0621   1C3D 90 03               BCC   DET2
0622   1C3F EE F3 17            INC   CNTH30
0623   1C42 AC 40 17    DET2    LDY   SAD        ; CHECK FOR END OF START BIT 
0624   1C45 10 F3               BPL   DET3
0625   1C47 8D F2 17            STA   CNTL30
0626   1C4A A2 08               LDX   #$08
0627   1C4C 20 6A 1E            JSR   GET5       ; GET REST OF THE CHAR, 
0628   1C4F             		         ; TEST CHAR HERE

What happens here:

– bit 7 (PB7) is tested until it becomes 0 (BIT SAD and BMI DET1 loop)
– the time is counted and kept in CNTH30 and CNTL30
– bit 7 is tested for becoming 1 (LDY SAD and BPL DET3)
– the rest of the character is read in by jumping into GETCH , the actual character received is not tested.

1006   1ED4             ;		
1007   1ED4             ;       DELAY 1 BIT TIME   
1008   1ED4             ;       AS DETERMINED BY DETCPS
1009   1ED4             ;
1010   1ED4 AD F3 17    DELAY   LDA   CNTH30     ; THIS LOOP SIMULATES 
1011   1ED7 8D F4 17            STA   TIMH       ; DETCPS SECTIONS AND WILL DELAY
1012   1EDA AD F2 17            LDA   CNTL30     ; 1 BIT TIME
1013   1EDD 38          DE2     SEC   
1014   1EDE E9 01       DE4     SBC   #$01
1015   1EE0 B0 03               BCS   DE3
1016   1EE2 CE F4 17            DEC   TIMH
1017   1EE5 AC F4 17    DE3     LDY   TIMH
1018   1EE8 10 F3               BPL   DE2
1019   1EEA 60                  RTS
1020   1EEB             ;		
1021   1EEB             ;                          DELAY 1/2 BIT TIME   
1022   1EEB AD F3 17    DEHALF  LDA   CNTH30     ; DOUBLE RIGHT SHIFT OF DELAY                              
1023   1EEE 8D F4 17            STA   TIMH       ; CONSTANT FOR A DIVE 2 
1024   1EF1 AD F2 17            LDA   CNTL30
1025   1EF4 4A                  LSR   A
1026   1EF5 4E F4 17            LSR   TIMH
1027   1EF8 90 E3               BCC   DE2
1028   1EFA 09 80               ORA   #$80
1029   1EFC B0 E0               BCS   DE4

The actual delay routines use the same logic as DETCPS. IN DEHALF the delay time is divided by 2 and jumped into DELAY.

KIM usernotes vol 06

Jim mcClahanan notes:

The PAL-1 (just like the KIM-1) uses a ‘soft UART’ or ‘bit banger’ for its serial I/O. I’m not a fan of this approach, but at the same time it demonstrates what could be accomplished with a minimial amount of hardware. The PAL-1 automatically figures out the appropriate delay between bits of the serial character when you press enter after a reboot. I have found that decreasing the value actually significantly improves the odds of an error-free load of larger punchtape format files. Below is a table for values found and suggest for $17F2.

Baud Found New
300 $EA $E8
1,200 $37 $35
2,400 $1A $18
4,800 $0B $0A
I haven’t tried to optimize the delay values. Right now I’m using 5 ms between characters and 500 ms between lines when doing 8K transfers and with the modified values I usually am successful. With the default values, it seemed like even with longer delays things would slip out of synchronization at some point more often than not on large transfers.

A subroutine that sends out an 8 bit character via the serial TTY output followed by one stop bit via bitbanging to PB7. Contrary to GETCH this allow 8 bits characters.
The receiving device should be set to 8N1 (8 databits, no parity, 1 stopbit)
Timing is done with the 1 bit DELAY routine.
A and Y are lost, X preserved.

What happens here?

– The character to send is stored at zeropage CHAR.
– save X
– A 1 bit delay, just to be sure
– set PB7 to the start bit 0
– a 1 bit delay
– get current value of PB7 (LDA SBD and AND #$FE)
– shift databit into carry (LSR CHAR)
– set carry to PB7 (ADC #$00 and STA SBD)
– delay 1 bit
– repeat for 8 databits
– set stop bit 1
– delay 1 bit, leave PB7 in rest state
– restore X

1200 baud, 20 ms character delay, 200 ms line delay is conservative but reliable for me. It is slow ..

An example for Teraterm is shown here:

KIM usernotes vol 06

Jim McClanahan

Serial Interface
The connector that came with mine is a male DB-9. Most USB serial interfaces (or interfaces on older computers) are also male DB-9 wired as the DTE device. The PAL-1 has the pinout of a DCE, which would normally have a female DB-9 connector. To get things connected, I used a “gender changer” (DB-9 female-to-female with pins 2, 3, and 5 connected straigt through).

The PAL-1 (just like the KIM-1) uses a ‘soft UART’ or ‘bit banger’ for its serial I/O. I’m not a fan of this approach, but at the same time it demonstrates what could be accomplished with a minimial amount of hardware. The PAL-1 automatically figures out the appropriate delay between bits of the serial character when you press enter after a reboot. I have found that decreasing the value actually significantly improves the odds of an error-free load of larger punchtape format files. Below is a table for values found and suggest for $17F2.

Baud Found New
300 $EA $E8
1,200 $37 $35
2,400 $1A $18
4,800 $0B $0A

I haven’t tried to optimize the delay values. Right now I’m using 5 ms between characters and 500 ms between lines when doing 8K transfers and with the modified values I usually am successful. With the default values, it seemed like even with longer delays things would slip out of synchronization at some point more often than not on large transfers.

The KIM-1 is a complete computer with two user interfaces and data storage with a simple namespace. It is one of the first 6502 computers, and many clones or derived 6502 SBC systems are designed with more or less KIM-1 copied parts of the software and hardware. On this site you can find many examples!

On the following pages I will try to explain how all this is working together. It will not be a rewrite of the KIM-1 user manual, please read that first, but more a deeper personal dive into the software and hardware of what the makes the KIM-1 tick. It also will expect a basic knowledge of the 6502, the 6530 and digital electronics.

The KIM-1 monitor software exists of two separate parts. The 6530-002 RRIOT ROM, called KIM as separate IC, RRIOT and the 6530-003 RRIOT ROM.
The two are not written as one program, the 6530-002 routines do not need the 6530-003.
One could speculate the 6530-002 software was developed together with the LED/keyboard display and TTY interface hardware. And when that design was done,
the need for data storage for the user arose and the 6530-003 was added.

The 6530-003 only has audio tape read and write routines and uses the ports of the 6530-002 for the audio bit streams.
The 6530-002 can be used to build a standalone computer, the 6530-003 is an addon for a 6530-002 based system.
Besides sharing RAM locations in the zeropage and the RAM area in the 6530-002 RRIOT the two do not use each others routines. The 6530-003 routines only know the address of the 6530-002 START routine.

Pages to follow:

• Execute a program: GOEXEC
• GETCH read a character from TTY
• NMI and IRQ and BRK
• OUTCH send a character to TTY
• Serial file transfer issues
• Startup of the KIM-1: RESET
• TTY DELAY routines
• Sigma, KB/TTY selection
• Suppress the KIM-1 echo
• Load papertape format

– architecture
CPU
RAM
RRIOTs
memory decoding
expendability and external access
– memory layout
– KIM-1 startup
– RESET routine
– TTY/KB selection
– the two user interfaces of the KIM-1
– TTY
hardware
routines
CLI
– LED display and keyboard
hardware
routines
CLI
– the KIM-1 file system and namespace
– the audio tape read
– the audio tape write
– missed opportunities in the KIM-1 design
– integration of main CLIs and tape routines
– tape read and write not callable as subroutines

Work in Progress July 6, 2026

Problems with the KIM-1 TTY character input

1. The KIM-1 hardware is hardware echoing incoming serial characters to the output, no echo in software involved, so you cannot influence what appears on screen. Very annoying!
2. The KIM-1 GETCH routine is blocking, no way to check for a character coming in, like a Break. waiting.
   Also quite annoying if porting other software to the KIM-1 or you want the program interruptable.
3. While a program is running something CPU intensive and you type something the program is not really waiting for, the characters appear on screen. Because the KIM-1 does hardware echoing of TTY input, this is unavoidable it seems

Here I present solutions for these problems in software, made possible by the genius hardware design of the KIM-1 TTY I/O.
You can have serial input wihout echo, non-blocking and even make the TTY input deaf for unwanted input.

Are they perfect? Maybe not, it is still bitbanging the incoming serial signal. It can miss the correct starting point for the incoming character bit stream.
If you want a perfect solution, you will need interrupt driven ringbuffered serial I/O with a dedicated IC like the 6850, 6511 etc.
Without this extra hardware you can achieve acceptable results with these routines.

Settings 2.3.1

I bought several products from RetroSpy.

• PAL-1 Motherboard Expansion Kit
• KIM-1 RAM/ROM Board
• MOS 6530 Replacement for the KIM-1 SBC
• Bus extender

Other interesting KIM-1/AIM 65/SYM- related boards on the Retrospy shop:
AIM 65 I/O board
SYM-1 I/O board
SYM-1 SymDos I/O board
SYM-1/AIM-65 RAM/ROM board
KIM-1 I/O board
2532 to 2764 EPROM adapter
SD Card Storage System (like the Corsham one)

I should have bought he KIM I/O card also, for the 1541 connector, next time!

My first encounter with Eduardo Casino was this topic on the German forum64.de forum in early 2023

If you do not read German: Eduardo, from Madrid, Spain!, announces his project to replicate a KIM-1 Rev D with the exact layout and look and feel as the original, using hires photos, Inkscape and Kicad.

This is not the first KIM-1 replica, as you can see here. What makes this replica special is that it is an exact PCB
replica. With curved lines! Other replicas may have the same dimensions and look and feel but use the straight modern PCB lines design.
He set a high standard and het continues to amaze us with hardware designs and software around the KIM-1. read all about on the follwing pages:

• KIM-1 rev D PCB redesign Eduardo Casino
• Dual 6532 adapter board
• KIM-1 keypad replacement

MTU replicas and additions

• MTU K-1008 Visable Memory Replica and MT motherboard

K-1008 Visable Memory Replica by Eduardo Casino

K-1013 Floppy Disk Controller replica

KIM-1 Motherboard for MTU Cards
KIM-1 RAM/ROM Expansion Board for the MTU Backplane
KIM-1 Programmable Memory Board for the MTU Backplane

CP/M-65

Version for the K-1013
KIM-1/PAL-1 version

KIM-1 Software

K-1008
XKIM
1541 OS

RAE was the name by Synertek for MAE, as ROMs for the SYM-1 which could be installed to add the Resident Assembler/Editor (RAE). Synertek contracted Eastern House Software to port their Macro Assembler/Editor (MAE) into an 8 KB ROM. AS you can see in the reconstructed source, the adaptations were not much more than adding the SYM-1 I/O such as character I/O and tape handling, the essence of MAE stayed as RAE. It was not that popular in the SYM-1 world, even Synertek used internally another assembler, with more MOS Technology compatible syntax.

The author of MAE and RAE, was Carl Moser. MAE was sold in various forms not only for the KIM-1 and SYM-1 but also for other 6502-based computers including Commodore, Atari, KIM, and Apple and in the Netherlands the Elektor Junior. Other forms of MAE included a cross assembler for 6800 and 8085.
Carl Moser and JR Hall were founders of Eastern House Software, the company that created several products for Atari 8-bit users, including Monkey Wrench and Monkey Wrench II, and the KISS word processor.

On topic on this site are the preserved KIM-1, SYM-1 and Elektor Junior versions. I have binaries, manuals and (reconstructed) sources for these versions for download.

Note that the manuals for the SYM-1 RAE are well written, and a good addition for the manuals of MAE.

On this page:

• KIM-1 Macro Assembler Editor
• Elektor Junior ASSM/TED
• SYM-1 RAE

• Catalogs and flyers Eastern House Software
• PC commandline tools to manipulate MAE/RAE files

Catalogs and flyers Eastern House Software

		Eastern House Software Catalog
		Eastern House Software Dealer Brochure
		EHS catalog 1985
		EHS catalog
		EHS flyer
		EHS Gazette 1981-03

PC commandline tools to manipulate MAE/RAE files

To get text into and out of the ASSM/TED program on the 6502 computer to the PC world,one can use several methods.
Written in Freepascal. Sources included, can be compiled in Linux etc.

The first method is using a terminal emulator and upload a text file or catch the output of the ASSM/TED program.
That gives some problems, mostly related to missing line numbers, or too much blanks.

Strip Blanks
The output of ASS/TED to the screen contains many blanks. When you want to uplaod the captured output, those blanks have to go

D:\myfiles\MAE\PC tools>StripblanksMoser.exe
V1.0 Strip blanks from captured ASSM/TED Moser source file
V1.0 Hans Otten, 2024
Syntax: StripBlanksMoser <sourcefile with blanks> <output source file to upload 
to ASSM/TED> [Y]
Y to overwrite outputfile without question asked

Add numbers
When you have a MAE/RAE source file without numbers, you can add those with this utility, increment of 10.

D:\myfiles\MAE\PC tools>AddNumbersMoser.exe
V1.0 Add numbers 0001-9999 to source file to make a ASSM/TED Moser source file
V1.0 Hans Otten, 2024
Add numbers 0001-9999 to ASSM/TED Moser source
AddnumersMoser <sourcefile without numbers> <output source file with numbers> [Y]
Y to overwrite outputfile without question asked

The other method is to dump or upload the text buffer as memory binary dumps.
Text is stored in memory as:
..
e.g.
the text
10 test
is stored as:
00 10 20 74 65 73 F3

RAE to TXT
Converts a binary MAE/RAE file to an ASCII text file without line numbers and normal line end

D:\myfiles\MAE\PC tools>RAEtoTXT.exe
V1.0 Convert a  ASSM/TED Moser RAE memory dump to text file
V1.0 Hans Otten, 2024
RAEtoTXT sourcefile memorydump output text file  [Y]
Y to overwrite outputfile without question asked

TXT to RAE
Converts a text file to binary RAE format, with line numbers.

D:\myfiles\MAE\PC tools>TXTtoRAE.exe
V1.0 Convert a  text file to ASSM/TED Moser RAE memory dump
V1.0 Hans Otten, 2024
TXTtoRAE <textfile > <output memorydump file  [Y]
Y to overwrite outputfile without question asked

How to dump or upload the the MAE/RAE text buffer

Dump

Start ASS/TED and add some lines

C 1979 BY C. MOSER


4163-53FC  5400-5EFC  5F00
4163  5400

10 test
20 lege regel
set

4163-53FC  5400-5EFC  5F00
4176  5400

Current (4176 in example above is to be stored at D3 (low), D4 (high))

BR to the KIM monitor and save 4163 to 4176 to a file, remember the end address, add that to the filename!
Upload

– Start ASSM/TED and BR to monitor
– Load the text file, place the end address in D3 (low), D4 (high)
– Enter ASSM/TED via the warm start at 2003 (KIM-1) or B003 (SYM-1)

Luckily we can build a KIM-1 clone that is either cheap and compatible, like the PAL-1, or a bit more authentic as the various KIM-1 boards.
Anyway, a clone has the KIM ROMs, and in E(E)PROM, to make it a KIM-1 clone. Altering is not done, you loose that unique spartan user interface!

The Apple 1 has also a monitor program, often called Wozmon to honor the genius of Steve Wozniak.

And you can combine both user interfaces on a not expanded KIM-1 clone!
I also included the Wozmon as a Setting in the KIM-1 Simulator.

Read more here!

The Apple 1 monitor (Wozmon) to be included in the empty space in the KIM-1 tape ROM

The Apple 1 and the KIM-1 are some of the earliest 6502 systems made.
Both are desirable, Apple 1’s sell for lots of $$$ and KIM-1s are getting more expensive.

Luckily we can build a KIM-1 clone that is either cheap and compatible, like the PAL-1, or a bit more authentic as the various KIM-1 boards.
Anyway, a clone has the KIM ROMs, in an E(E)PROM, to make it a KIM-1 clone. Altering is not done, you loose that unique spartan user interface!

The Apple 1 has also a monitor program, often called Wozmon to honor the genius of Steve Wozniak.
And you can combine both user interfaces on a not expanded KIM-1 clone!
Ronny Ribeiro, a user of a PAL-1, saw that the KIM tape ROM has quite some unused space. In a real KIM-1 that is wasted, you cannot program the ROM.
In a clone you can. He saw that that free space is large enough to hold the Wozmon, adapted a bit for the KIM-1 TTY I/O.
He offers a ROM image for a clone, with the Wozmon built in at 1AA0. And added a command to go back to the KIM-1 monitor.
He also used the ROM with the ‘KIM’ prompt in his system with ‘PAL’.

I moved wozmon in the original KIM ROMs in 2K image with Wozmon in the tape ROM empty space.

Start Wozmom at $1AA0, used buffer at $0300

Based upon the ideas and work of Ronny Ribeiro.
Source included. Standard 6502 assembler, I used TASM32

The KIM-1 Simulator is used to test this. And this Wozmon is now available in Settings!

Here I offer you that ROM. I reconstructed the source and added the result to the KIM-1 ROM image. WIthout the KIM prompt change!
In the archive you find source etc of the Wozmon for KIM, the binary ROM image to load in the KIM clone rom, the Wozmon for KIM-1 source and a small userguide by San Bergmans.