KIM-1 printer output RS232 H14

Original articles KIM Kenner 13 1980, 6502 Kenner 19 1981: Hans Otten PGJ de Beer Trasnlated Hans Otten 2021

In two articles a routine to send a character via serial to a printer (or any serial device) and interface this routine to Micro Ade.
The second version allows for handshake signal CTS.
Baudrate may vary from 300 to 9600 baud. Only one or two (handshake) PIA bits are nevcessary, the serial signal is composed with bit banging.
A simple hardware connection to RS232 in two variants: RS232C signal level compliant or a very simple resistor (sufficient for short distances and most printers).

Source in Micro Ade format.

First source with choice of baudrate, second fixed baudrate 4800 baud and CTS handshake.

Also a routine to read a character form a parallel keyboard connected to PIA A with strobe bit in bit 7.

Make MS Basic KB9 faster: the ROR bug

KIM Kenner 19 Patches op Basic Hans Otten, translated by Hans Otten, 20211

May 1981 Byte Magzine had an article in System Notes, Faster Basic for Ohio Scientific.
The article described how the first batch of the 6502 had a faulty ROR instruction, so the programmers of Microsoft Basic had to work around this missing instruction with a slower replacement, (Note 2021: this is well explained in the Pagetable MS Basic articles) and how to patch this to really use the ROR instruction and speed up things.

A letter to the editor in a later Byte (September 1981?) showed the patches required for the KB9 KIM-1 version.

Location $37DE to $3801 and $38D2 to $3903 are now unused.

This patch may speed up KB9 quite a bit for number crunching.


Cassette read and write indicator

KIM Kenner 10 March 1980, Dutch article by Hans Otten, English translation Hans Otten, 2021

Having an indication of how the reading and writing to the cassette recorder is going is nice. With the Micro Ade routines the LED display is used for this. the standard KIM-1 routines are mute.
This small hardware circuit gives either a visual or audible indication with the standard KIM-1 routines.

How does it work?
An indication for for the read process is the output signal of the PLL circuit, a stream of digital pulsed delivered at PB7 of the RRIOT 6530-002. During the reading pin PB7 is rpogrammed as input, during the wirte it is an output. Via a buffer the output signal signal is brought to Audio-Out and Audio-Out-High.
The use of PB7 as input and output during the read and write process means that during a read the decoded signal appears on Audio Out, and as it is meant to be, during writing also has the output signal. Collision is prevented by blocking the input signal during writing. So this means that during reading and during write the signal is present on Audio-Out. This enables a indication of both read and write processes.

The circuit

The signal on Audio-Out (application connector A-M) is brought to a transistor (general purpose type) and the alternating signal makes the LED blink quite fast. A miniature loudspeaker can be switched in and the signal can be heard, it is in the hearable audio range. The LED is not very informative, the loudspeaker is, but also can be annoying, so the switch is welcome.

Do not use a lower value than 33 ohm for R2, it will damage the transistor. The circuit does not represent a heavy load, so you can use the KIM-1 power supply.

A piece of stripboard is sufficient. See the figure below for the connections of transistor and LED. Red, green, yellow can all be used.
Other usage
By programming the output PB7 music or signals can be heard.

Reading tapes from other KIM-1

KIM kenner 6 1978 Hans Otten Dutch, translation to English Hans Otten 2021

Reading tapes recorded on another KIM-1 or bought like Tiny basic, Microsoft KB-9, Miccrochess and Micro Ade was not that easy. Many many errors, especially the hypertape format.

Reading and writing of my own tapes, after having configured the PLL following the guide in the User manual, and keeping the cassette recorder clean, now is flawless. With the motor control (see Micro Ade manual appendix) it is a pleasure!

I read and tried all advices, like adjusting the azimuth of the recorder head, cleaning etc. Maybe the variations in tape speed between recorder and my player and the resulting frequency shift was a problem?
What really helped was looking with an oscilloscope at the output of the PLL (pin 7 of the LM311) we can see clearly the problem:

No real problems with noise or dropouts, just deviations between different recordings, so the PLL does not operate correctly. Bought tapes showed the pictures Wrong 1 and Wrong 2. And that leads to reading problems, the software makes the wrong decisions on ‘0’s or ‘1’s.

The following procedure was developed to read the bought tape, store it and save the program on my own tapes:

  1. Start reading the problem tape, 1873G
  2. Connect a simple voltmeter to pin 7 of the LM311 or Expansion connector-X
  3. Now change the PLL variable resistor to a reading of 2.7V. A scope would show ‘Correct’
  4. Start the read again
  5. Save the program
  6. Repeat with your own recording or the user Manual PLL set procedure

This helped me to read the problem tapes. Only for Microsoft Basic I had to play with the output volume, large variations in the recorded signal. But it worked in the end and now I have my own recordings on tape, several stored and working copies. One can never have enough backups!

PLL Test

This program write alternate two low frequency or three high frequency tones to the tape recorder.
Record this for a couple of minutes.
When reading this tape the PLL should convert this to a symmetric block pulse.

This program shows on the first two digits on the KIM-1 LED display the number of ‘1’s read, on the second two digits the number of ‘0’s read.
When all is well this should 80/80 but anything between 60/A0 and A0/60 is fine.

ASCII parallel keyboard to KIM-1

Kenner 2 page 4 July 1977 Co Filmer, translated to english Hans Otten, 2021

A parallel ASCII keyboard is a nice addition to the KIM-1.

Connect to the PIA A of the KIM-1 on the Application connector.

Some keyboards may require a -12 V power supply.

The address 1700 now shows the ASCII keyboard code of (the last) key pressed. The high bit (PB7) is the strobe signal, the other 7 bits the ASCII code.

A program should poll the strobe bit, if activated wait for the strobe bit to be deactivated, and then read the key and return.
Testing for keypressed such as a break test means checking the strobe bit, if activated stop processing, etc..

Code fragments by Hans Otten

   ; example of break test
 BPL GOON ;     WHILE NOT keypressed
 JMP MONRET ;      
GOON continue processing

Cassette reading problems KIM-1

Another article from the Dutch KIM Kenner magazine:

RECORDING PROGRAMS WITH THE KIM-1 AND THE CASSETTE RECORDEROriginal Uwe Schroeder, KIM Kenner 1, March 12 1977 Translation June 2021 Hans Otten

Recording programs with the KIM-1 and the cassette recorder

Original Uwe Schroeder, KIM Kenner 1, March 12 1977  Translation June 2021 Hans Otten


A large number of KIM-1 users seem, like me, to have problems recording computer programs on the cassette recorder. For unknown reasons the KIM-1 refuses to read a program, while before it went well with the same tape. These problems have led me to study the KIM-1 system and I hope to have finally discovered the cause of the problem.
This article serves to aid other KIM-1 users to solve also these problems.

Part of the PLL circuit, including input impedances

Analysis of the KIM-1 FSK system
Signals are stored on the cassette tape with FSK (frequency Shift Keying). By consecutive high and low frequency sounds (on the KIM-1 3.6 kHz and 2.4 kHz). These high and low frequency sounds are generating not with much hardware, but with software. Reading programs is done by analyzing these sounds with the LM565 IC (a Phase Locked Loop, see User manual page 31 and fig 3.8). The fact if the sound was high or low frequency is determined after some amplification and filtering via a LM311 comparator to ‘0’ and ‘1’ and offered to I/O port PB7 of the second 6530 RRIOT).

The problems arising at the reading are probably caused by not correct functioning of the circuit around the PLL. The average cassette recorder appears to supply sometimes during a very short period a dropout to let the PLL function correctly.

Where and how things can go wrong with the PLL

  • When we record on the cassette recorder a constant tone of 3.6 kHz and listen to the recording and examine it with an oscilloscope, we see and hear the sound volume fluctuate or even disappear for short periods, we call this dropouts of the tape. These dropouts will mean a fluctuation of the sound available for the PLL to detect 10 to 100 times lower volume and cause the detection to fail. By measuring the PLL level I have seen 10 to 100% more signal than required, so that ca mean PLL malfunction.
  • If a tape is passing the head misaligned/tilted of the tape recorder head, higher frequencies are in the disadvantage and weaker. This head misalignment will cause problems with recordings from other tape recorders, bought or from other users.
  • Suppose we use a perfect +5V power supply, then VCC can be considered ‘Ground’ When we send on Audio In a AC current of 550 mV, then resistors R8 andR14 reduce the signal 1/11 of 550 Mv = 50 mV supplied to the PLL. Measurements indicate the PLL requires at least 40mV to sync the PLL and see it as a ‘high’ frequency sound.
    Remark: replace the R8 with 1K to give the PLL 250 mV instead of 50mV.
  • Suppose we use a perfect recorder with a very low output impedance. And suppose the power supply has a noise level of 600 mV. Fig 2 shows, after some calculations the noise level results in 40 mV on the PLL input. If we reduce the resistor to 1K , the noise level becomes 230 mV.

The specifications of the PLL indicate the correct functioning of the PLL at an input level of nominal 2, maximal 20 mV. The fact that the measurements indicate the PLL only operates at levels of 40 mV indicate the noise levels are at the same level as the input signal coning from the recorder. A better noise reduced may help, but other sources of interference are possible. Therefore extra amplification of the signal is preferred instead of altering the KIM-1 hardware.

Solve the tape recorder problems
Since the problems with reading of tapes on the KIM-1 seems to be related to fluctuating signal levels:

  • Record the signal as loudly as possible, use a recorder without automatic level adjustment and record so that the tape is saturated.
  • When using the loudspeaker output, experiment with the volume. But too loud means distortion and may also lead to failures.
  • Build an amplifier for frequencies 2-4 kHz 10 to 20 times, short dropouts should be well amplified.
  • Use C60 instead of C120 types. Normal cheap ferro is fine, Chrome has more dropouts.
  • If the KIM-1 reports a reading error (FFFF in the display) and you want to know how much of the tape has been read, location 17ED and 17EE contain the first address not read yet.
    Make a copy of finished programs on another cassette and check this copy for readability. Do not use this copy anymore and store it. When using a cassette often, this may lead to problems, like the mangling of the tape in the drive.

Here is a procedure to work around reading tape problems:

  1. Check if the recorder is connected to the KIM-1
  2. Check Volume and Tone control ((max high)
  3. Press Reset.
  4. Set location 17F9 to 0.
  5. Set location 00F1 to 0.
  6. Inspect location 1742. Here the information of I/O pin is shown. The display shows 1742 87
  7. Start the recorder. The middle bar of the 8 now will blink, if not : you have Error 6A (see below).
    Stop the recorder, remove the cassette and start the recorder. Now the middle bar of the 8 should not blink, else you have Error 6B (see below)
  8. If the Volume knob of your recorder controls the strength of the output signal: start the recorder and determine in which setting the blinking of the bar changes. If you have not enough headroom, see Error 7.
  9. Check of the correct detection of the high frequency.
    Type in the next program and start it (the program writes a constant tone of 3.6kHz to the recorder)
    Record this tone on the recorder for several minutes.
    Rewind the recorder and start playing. Now the display should show no middle bar 1742 07
    The bar should not blink at all, every blink indicates a dropout or such. See Error 7 and Error 8.
  10. Read User Manual C and E

Oscilloscope test
If you have an oscilloscope, do the following measurements.

  1. Attach the scope to Audio Out, e.g the negative side of C4 (user manual page B-1).
  2. If you have dual channel scope, connect the other input to the top of resistor R8, that is the PLL input.
  3. Set the timebase to 1 ms, and connect Audio-Out-High with Audio-In.
  4. Start a dump of memory with 1800G

The scope will now show figure 3.

Stop the dump program , remove the connection between Audio-In and Audio Out-High and connect the cassette recorder to the KIM-1. Start reading the tape (1873G) and move the tape to a problem area. You need to start the reading program to avoid the interference of the display. When all is right you should see the same nice picture on the scope as before.
Now increase and lower the signal level of the cassette recorder to see, if or when, there are problems with the PLL. Dropouts are visible with a image that is unstable or noise peaks. Dropouts are best studied with the 3.6 kHz recorded signal. They are visible as negative peaks on Expansion connector PLL-Test E-X. A high frequency tone is on this pin a +5V, a low as 0V.

Error 6A
The PLL is not functioning, sounds are not detected. This can be caused by:

  • No +12V power supply
  • The signal of the cassette recorder is not reaching the KIM-1
  • The signal is way too weak
  • The PLL is broken or not properly configured.
    Configuring of the PLL can be done with the program PLLCAL in Appendix I page 13
    Connect Audio-Out-High with Audio-In and start the test program on 1A6B. Inspect pin E-X PLL test on the expansion connector with a voltmeter. Adjust the variable resistor on the KIM-1 so that you see 2.5V. A small adjustment can lead to 0 to 5V, as expected.

Error 6B
The PLL is active while no input signal is present.

  • Noise signals picked up
  • Defective PLL or misconfigured of the display shows: 1742 07

Error 7
Your cassette recorder is delivering a too weak signal and you will get reading problems. See the amplifier below for a solution.
Error 8
Essential for the correct operation is the correct high frequency 3.6 kHz.

  • Dirty cassette recorder heads. Clean with a quality product
  • Unaligned head. If you are lucky there is aa small screw next to the tape head allows to adjust it, listen to a high pitch
  • Tape head is worn out, replace the cassette recorder

Amplifier between KIM-1 and the cassette recorder.

When some amplification is required the following circuit may be useful.

The amplification is controlled with variable resistor P1 from 3 to 100x. A second order Butterworth filter lowers frequencies below 2 kHz to remove mains noise.
Note the shielded cables in the drawing. Be careful to use the indicated ground point, never make a groundloop !
Place the amplifier away from noise sources and the KIM-1, noise will be amplified too!

Insert a 22 nf (22kpF in the drawing) on resistors R33 and R34 (see figure 4 right bottom and Appendix B page B1).
Adjust P2 variable resistor for Vu (output 741 opamp) = 6V
P1 controls the amplification.
The opamp (741) can be any standard general purpose audio type.
Test the amplifier as described above. Adjust for optimal volume. Record a program on tape with lower as usual volume. Try higher volume only temporarily if an error occurs.

Suppress KIM-1 echo

Original article: KIM Kenner 17 page 14, Dutch, Hans Otten. Translation 2021 Hans Otten

Problem: the KIM-1 hardware is echoing incoming serial characters to the output, no echo in software involved. Very annoying!

In the KIM Kenner 1 Siep de Vries, founder of the Dutch KIM Club mentioned how in Focal for the 6502 a trick was built in to suppress the hardware echo by manipulating the TTY out bit. From the Focal disassembly:

34B1  2C 40 17          BIT H1740
34B4  30 F9             BMI H34AF       ;=>
34B6  AD 42 17          LDA H1742
34B9  29 FE             AND #$FE
34BB  8D 42 17          STA H1742
34BE  20 5A 1E          JSR H1E5A
34C1  48                PHA
34C2  AD 42 17          LDA H1742
34C5  29 FE             AND #$FE
34C7  09 01             ORA #$01
34C9  8D 42 17          STA H1742
34CC  68                PLA
34CD  18                CLC
34CE  60                RTS

Hardware echo

I took the idea and implemented the software (wihtout knowing then in 1980 the Focal disassembly!).

The echo of incoming serial to outgoing is shown in the next figures (from the KIM user manual and the KIM Circuit poster).

The TTY KEYBD signal goes via a transistor and NAND gate U15 to PA7 port of the 6532. That signal also goes to pin 10 input  of NAND gate U26  which is the TTY out line. This is the hardware echo. When the KIM-1 sends out a character it comes  from PB0 to pin 9 of of NAND gate U26 and so comes out to the TTY Out line.
Note that PB5 is connected via an inverter to NAND gate U15. The other input is TTY IN. Making PB5 high will make the TTY input PA7 deaf.
Note PB5 is also Audio out.

Suppress echo in software

The solution to suppress the echo is making output PB0 low. The NAND gate out will now stay high, ignoring any changes on the other input, which is the incoming serial character.
Only when receiving a character PBO should be made high. Also any incoming character will now not be echoed unless the program wants to receive a character!

Example program

In this routine the standard KIM-1 GETCH routine at $1E5A is encapsulated in a subroutine that prevents the echo by setting PB0. Note that this is not a complete block of the echo, it is only active when the program calls the blocking EGETCHAR. When the program sends out charactersto a dispaly, anything typed at the keyboard will also appear at the display.
The calling program is now responsible for the echoing!

0001   1000             echo .org $1000
0002   1000             ;
0003   1000             echoflag = $17E2 ; flag: 0 normal echo
0004   1000             SBD = $1742 ; KIM 6532 PIA B data register
0005   1000             GETCH = $1E5A ; KIM TTY Getch routine 
0006   1000             ;
0007   1000 AD E2 17    EGETCHAR LDA echoflag ; if notechoflag 
0008   1003 F0 08         beq normal ;  then normal echo 
0009   1005 AD 42 17      LDA SBD  ; else set TTY bit PB0 to 0 
0010   1008 29 FE         AND #$FE  
0011   100A 8D 42 17      STA SBD ; 
0012   100D 20 5A 1E    normal JSR GETCH ; get character from input
0013   1010 48            PHA ; save
0014   1011 AD 42 17      LDA SBD ; set TTY bit PB0 
0015   1014 09 01         ORA #$01 
0016   1016 8D 42 17      STA SBD 
0017   1019 68            PLA ; restore received character
0018   101A 60            RTS 
0019   101B               .end
0020   101B               tasm: Number of errors = 0

Does EGETCHAR work on the KIM-1 clones?

Micro-KIM and PAL-1: yes, the hardware is identical, IC numbers are different
Corsham Technology: yes, though the hardware for audio is not there, there is still a NAND gate IC17C coupling PA7 and PB0.

Enhanced solution: always deaf for input
If you study the hardware shown above you see PB5 also blocks the echo. The following routine tries to use this to make the input permanent deaf.

0001   1000             echo .org $1000
0002   1000             ;
0003   1000             echoflag = $17E2 ; flag: 0 normal echo
0004   1000             SBD = $1742 ; KIM 6532 PIA B data register
0005   1000             GETCH = $1E5A ; KIM TTY Getch routine 
0006   1000             ;
0007   1000             ; no echo when reading character
0008   1000             ; 
0009   1000 AD E2 17    EGETCHAR LDA echoflag ; if not echoflag 
0010   1003 F0 08         beq normal ;  then normal echo 
0011   1005 AD 42 17      LDA SBD  ; else set TTY bit PB0 to 
0012   1008 29 FE         AND #$FE 
0013   100A 8D 42 17      STA SBD ; 
0014   100D 20 5A 1E    normal JSR GETCH ; get character form input
0015   1010 48            PHA ; save
0016   1011 AD 42 17      LDA SBD ; set TTY bit PB0 
0017   1014 09 01         ORA #$01 
0018   1016 8D 42 17      STA SBD 
0019   1019 68            PLA ; restore received character
0020   101A 60            RTS 
0021   101B             ;
0022   101B             ; no echo only at wish if reading character
0023   101B             ; note that using tape I/O will leave PB5 low
0024   101B             ; 
0025   101B AD E2 17    DGETCHAR LDA echoflag ; if notechoflag 
0026   101E F0 05         beq dnormal ;  then normal echo 
0027   1020 AD 42 17      LDA SBD  ; else set TTY bit PB0 to 
0028   1023 29 FE         AND #$FE ; PB0 low
0029   1025 29 DF       dnormal AND #$DF ; PB5 low
0030   1027 8D 42 17      STA SBD ; 
0031   102A 20 5A 1E      JSR GETCH ; get character from input
0032   102D 48            PHA ; save
0033   102E AD 42 17      LDA SBD ; set TTY bit PB0 and PB5
0034   1031 09 21         ORA #$21 ; high
0035   1033 8D 42 17      STA SBD 
0036   1036 68            PLA ; restore received character
0037   1037 60            RTS 
0038   1038               .end
0039   1038               
0040   1038               tasm: Number of errors = 0

Note that using tape I/O will leave PB5 low, allowing echo, only set high when the program calls DGETCHAR.

Does DGETCHAR work on the KIM-1 clones?

Micro-KIM and PAL-1: yes, the hardware is identical, IC numbers are different
Corsham Technology: no, PB5 is not used.


Convert to Papertape V2.2

On the Utilities page I have two programs to convert to MOS Technology papertape format: KIMpaper, a command line utility, and ConvertHexFormat, a GUI app.

All in Freepascal/Lazarus source format, and tested on Linux (Raspberry PI OS) and Windows 10 64 bit. So the programs will run everywhere Lazarus is available (MS DOS, WIndows, Linux Mac OS).

KIMPAPER  is written at the time the Micro-KIM appeared. CLI utility.  Supports Binary to/from Papertape.  Still runs fine on all platforms supported by Freepascal (Windows, MS DOS, Linux etc) after a recompilation, source available.

ConvertHexFormat is a more recent GUI utilitilty with many more 8 bit hex formats as input and output.

There were some bugs of course in older versions. V2 added the ability for multipart hex formats, records having a non-consecutive load address. That seems to wok fine since V2.1
In 2.2 a bug in MOS Papertape format for bigger files is fixed, the end-of-file record (record type 00, total line count) had a bug in the checksum calculation. KIMPAPER is and was correct in the calculation.
But in ConvertHexFormat it was wrong (as it still  is in the well known srec utility in the Unix world!).