KIM-1 Simulator breakpoints and watches

The KIM-1 Simulator is updated to version 0.10.1.

Changes in this version are an extension to the “Run to” execution

    • up to 10 breakpoints are now possible instead of one
    • up to 10 watch points addresses. When the CPU accesses the watch point execution stops
    • Save file to memroy bug fixed (thank Nils!)

Watch and breakpoints can be enabled or disabled at will, even while the program is running.

Serial terminal emulation software

Serial terminal emulation software, essential when working with SBC’s like the KIM-1.

I started working with computers long long ago. I loved the Digital Equipment devices, the VT100 (1982!), the excellent VT220, the VT340. All serial, the base of the ASCII control codes.

A wide selection is available of programs that work with the serial line.

    • Most implement a subset of the ASCII control codes, VT100 and more. for SBC’s a subset is sufficient
    • Some have strengths in debugging and showing what is sent or received (hex view, control characters etc).
    • Also important is flow control (off, hardware/software).
    • Sending/receving files (text or binary) is also often the only way to get data to/from the SBC. Simple character based (includes hex formats like Intel, S records Motorola, MOS papertape) or with a protocol (Xmodem, Ymodem. Zmodem etc).
    • TCP?ip protocols like SSH are a bonus
    • And last but not least the ability to wait/delay after sending a character or Line end (Enter key) to let the slower SBC handle the incoming data. For example the KIM-1 MOS papertape format receive, but at higher baud rates needs delays

I found a page on Sparkun that has an excellent description what is essential in dealing with serial communication on a PC, be it Windows, Linux etc.

Also this page names good free terminal emulation programs, running as GUI programs, for serial I use myself.
– Coolterm (croos platform)
– Tera Term (Windows)
– Realterm (Windows)
– YAT (WIndows)

Not named in this list

– Putty (linux and Windows)
– Minicom (Linux console mode)

KIM-1 and clones

Most programs allow character and line delay for sending to slow devices. The KIM-1 with its bit banging serial routines is one of them.

For me 9600 baud, 5 msec character delay and 100 msec line delay worked for me to upload papertape format, this also applies to the clones like PAL-1, Corshams KIM Clone and the Micro KIM.
For Microsoft Basic text file uploads of program sources a line deay of 200 msec may be required.

Serial ports

Nowadays serial ports are only available with USB devices. Work fine in general.

On my other website I have information on USB serial communication and how to write programs (Lazarus of course).

PL2303HX misery
USB serial adapter testing

Elektor Junior Paperware 3 in German!

Thanks to Martin Seine I have added the Paperware 3 in German book to the Junior book collection.

6502 Microprocessor KIT

I have a 6502 system that looks a lot like the Microprofessor 1.

Have been playing with it, a new version of the monitor and using the serial I/O. So an update to the page devoted to this system.

Atari 850 interface: 6507 + 2 6532

Though this site is not about home computer systems, but about small SBC’s, it is nevertheless interesting to look at the Atari 850 system.
Atari produced the 850 Interface Module to provide access to devices complying with two important interface standards of the time, RS-232-C serial and Centronics parallel.
Four serial interfaces, one parallel interface in self contained case, with its own power supply. Connected to the Atari via the standard SIO cable.

When you look into the system you discover it is actually a simple microprocessor system. The heart is a 6507 CPU, the serial and parallel lines are built with two 6532 IC’s, a ROM with the software.Serial interfaces and the 6532? This means bit banging.So this fits well in the theme of small SBCs!

Atari 850 interface: 6507 + 2 6532

Though this site is not about home computer systems, but about small SBC’s, it is nevertheless interesting to look at the Atari 850 system.
Atari produced the 850 Interface Module to provide access to devices complying with two important interface standards of the time, RS-232-C serial and Centronics parallel.
Four serial interfaces, one parallel interface in self contained case, with its own power supply. Connected to the Atari via the standard SIO cable.

When you look into the system you discover it is actually a simple microprocessor system. The heart is a 6507 CPU, the serial and parallel lines are built with two 6532 IC’s, a ROM with the software.
Serial interfaces and the 6532? This means bit banging.
So this fits well in the theme of small SBCs!

I show you here the circuit diagram, operator, service and technical manual and the sources/binaries of the ROM.

Circuit diagram
Atari 850 interface Module Operator Manual
Atari 850 interface Module Technical Manual
Atari 850 interface Module Service Manual
Sources and binaries of the 850 ROM
Parts list page 1, 2

While the Atari's SIO and controller ports did not conform to established
industry standards, Atari produced the 850 Interface Module to provide access
to devices complying with two important interface standards of the time,
RS-232-C serial and Centronics parallel.

RS-232-C Serial Interface
The Electronic Industries Association (EIA) introduced the RS-232 standard,
entitled "Interface Between Data Terminal Equipment (DTE) and Data Circuit-
Terminating Equipment (DCE) Employing Serial Binary Data Interchange," in 1960
in an effort to standardize the interface between DTE (usually a terminal or a
computer emulating a terminal) and DCE (usually a modem).  Although emphasis
then was placed on interfacing between a modem unit and DTE, other
applications for the standard gained popularity.  Early versions of the EIA
232 standard included RS-232 (1960), RS-232-A (1963), and RS-232-B (1965).
From 1969-1987, including most of the time of the 8-bit Atari, the standard
was formally known as EIA RS-232-C.  Revisions since then have included EIA-
232-D (1987), EIA/TIA-232-E (1991), and the current version from the
Telecommunications Industry Association, EIA/TIA-232-F (1997), known as of
2011 as TIA-232-F.  Especially in the 1980s, 232 was widely adopted for low-
cost serial connections between the DTE and peripherals such as an external
modem, mouse, plotter, printer, scanner, digitizer, track ball, and myriad
others.  In more recent years TIA-232-F has essentially been supplanted by
USB.  In keeping with the context of the time period, this FAQ will normally
refer to the 232 standard as RS-232-C.  

The Atari 850 interface connects to the SIO port on the Atari computer and
provides the system with:

- Four serial interface ports (RS-232-C)
- One 8-bit parallel output interface port (Centronics)

Serial interface port key features:
- The 850 functions as RS-232-C Data Terminal Equipment (DTE).
- RS-232-C Circuits (signaling lines):
                 (Send / Out)  | (Receive / In)
       Port 1:   XMT, DTR, RTS | RCV, DSR, CTS, CRX
       Port 2:   XMT, DTR      | RCV, DSR
       Port 3:   XMT, DTR      | RCV, DSR
       Port 4:   XMT           | RCV
- Port 4 primarily serves as a 20 mA current loop interface, supporting
  20 mA current loop peripherals such as a teletype machine.
- Baud rates:
    45.5 bit/s*, 50 bit/s*, 56.875 bit/s*, 75 bit/s**, 110 bit/s, 134.5 bit/s,
    150 bit/s, 300 bit/s, 600 bit/s, 1200 bit/s, 1800 bit/s, 2400 bit/s, 
    4800 bit/s, 9600 bit/s
  * These baud rates are useful for communications with Baudot teletypes, for
    RTTY (radioteletype) applications.  They are more commonly referred to as
    60, 67, and 75 words per minute.
 ** This baud rate is sometimes used for ASCII communications, and may also
    be used for 5-bit Baudot RTTY.  The latter is commonly referred to as
    100 words per minute.

The Atari Operating System does not include a resident device handler for the
serial ports of the 850, but the 850 contains an R: handler, supporting
devices R1: through R4:, in its ROM.  
   - Bootstrap without disk drive-- With no powered disk drive #1 present, the
     R: handler loads from the ROM of a powered 850 into computer RAM on 
     system startup.  (The 850 masquerades as disk drive #1, responding to the
     Atari OS attempt to boot from disk.)  An extended beep is emitted through
     the computer's audio signal as the handler is loaded.
   - Bootstrap with disk drive-- The R: handler can be loaded from the
     850 ROM as part of a Disk Boot.  (Atari DOS 2.0S, DOS 3, DOS 2.5, and 
     DOS XE include provisions for this.)
   - The R: handler can be loaded from the 850 ROM by software after system 
Many alternatives to the 850 ROM R: handler have been developed.  Please see a
separate section of this FAQ list regarding R: and T: device handlers for the
850 for more details.

The Atari Operating System's resident P: Printer device handler supports the
parallel output interface port of the 850.
- 400/800 OS: Responds to P: and ignores any device number
    XL OS: Responds to P:, P1:, and P2:

Serial Interface Port 1 (DE-9 Socket - female):
                1. DTR Data Terminal Ready (Out)
                2. CRX Carrier Detect      (In)
  5         1   3. XMT Send Data           (Out)
   o o o o o    4. RCV Receive Data        (In)
    o o o o     5. Signal Ground
   9       6    6. DSR Data Set Ready      (In)
                7. RTS Request to Send     (Out)
                8. CTS Clear to Send       (In)

Serial Interface Port 2 (DE-9 Socket - female):
  5         1   1. DTR Data Terminal Ready (Out)
   o o o o o    3. XMT Send Data           (Out)
    o o o o     4. RCV Receive Data        (In)
   9       6    5. Signal Ground
                6. DSR Data Set Ready      (In)

Serial Interface Port 3 (DE-9 Socket - female):
  5         1   1. DTR Data Terminal Ready (Out)
   o o o o o    3. XMT Send Data           (Out)
    o o o o     4. RCV Receive Data        (In)
   9       6    5. Signal Ground
                6. DSR Data Set Ready      (In)

Serial Interface Port 4 (DE-9 Socket - female):
                        / 20 mA Current Loop Operation
                1. +10V / TXD+ Send Data +
  5         1   3. XMT  / TXD- Send Data - (Out)
   o o o o o    4. RCV    Receive Data     (In) --+  A 20 mA current loop
    o o o o     5. Ground                         |  device must tie together
   9       6    7. +10V / RXD+ Receive Data +   --+  pins 4 and 7.
                9. -8V  / RXD- Receive Data -

Parallel Interface Port (DA-15 Socket - female):
                     1. /Data Strobe
                     2. Data bit 0
                     3. Data bit 1
 8               1   4. Data bit 2
  o o o o o o o o    5. Data bit 3
   o o o o o o o     6. Data bit 4
  15            9    7. Data bit 5
                     8. Data bit 6
                     9. Data Pins Pull-Up (+5V)--+ A device that cannot hold
                     11. Signal Ground           | /Fault high may instead tie
                     12. /Fault (high required)--+ together pins 12 and 9.
                     13. Busy
                     15. Data bit 7

Prototype 850 units are in an all-black brushed steel case, but production
units are in a beige plastic case matching the 400/800 computers.

Front of unit (left-to-right):
 - Power In jack
 - On power indicator light
 - Power Off / On switch
 - Two I/O Connectors (Atari SIO)
Right side of unit:
 - Parallel Interface port
Rear of unit (left-to-right):
 - Four Serial Interface ports, 4 - 3 - 2 - 1

850 internals:
 - 6507 MPU (MOS Technology MCS6507 or equivalent), C010745
 - 6532 PIA.  Two of: 
    - MOS Technology 6532 RAM-I/O-Timer (RIOT) or equivalent, C010750
 - 4KiB X 8 Bit ROM, C012099

- Atari 850 Interface Module Operator's Manual C015953 Rev. 1 1980
  (preliminary version shipped with earlier/most 850 units; 102 pages)
- Atari 850 Interface Module Operator's Manual C017651 REV. B 1982 (15 pages)
- Atari 850 Interface Module Technical Manual C017652 REV. B 1982 (106 pages)
- Atari 850 Interface Module Field Service Manual
   - CS 400/800-S004-B 4/81
   - FD100036 April, 1981

Power: Used with an external 9 volt AC transformer power supply rated for at
least 17 watts: Atari CA014748 or equivalent.

The 850 was designed by R. Scott Scheiman at Atari, 

The 850 was alo sold as bareboard with a parts list

KIM-1 emulators

A page describing known (to me) KIM-1 emulators.

No one is yet prefect., the combination of my KIM Simulator and the KIM-1 emulator in Javscript comes close.

KIM-1 emulators

A list of KIM-1 emulators/simulators
To be included in this list, the emulator should run the original KIM-1 ROM’s. I prefer to see source code, which all do except Kimplement. If I can not run it, it is not on this list (I know of an Apple iPhone  and a Palm Pilot version) .

My favorites are of course my own KIM Simulator (for TTY programs) and the KIM-1 emulator in JavaScript (for LED display programs).

Troublemakers in KIM-1 emulation are due to the bit banging nature of the KIM-1 system:

  • Serial I/O.
    Since the KIM-1 uses bit banging to do serial I/O this is hard to emulate. Therefore msot emulators patch the ROM at the GETCH and OUTCH locations to send and receive a character, including the hardware echo of GETCH
  • The automatic baudrate detection, also a bit banging routine, is patched out since it has no meaning with patched serial I/O routines and makes the emulator hang at boot.
  • Break detection.
    Most KIM-1 programs, like MS-Basic, break/stop detection by a BIT at location $1740. This of course does not work on patched serial I/O, so a patch at location 1740 is required.
  • The finer details of the serial interface, like PB0, PB5, PB7 and PB7 are often not implemented, so the hardware echo can not be prevented.
  • Tape I/O, $1800, $1873, is often replaced by some form of dumping /loading memory with the start and stop and ID of the original routine with a binary file or omitted
  • LED displays.
    Also bit banging. By calling the SCANDS routine, repeated at a fast rate, the LED segments are switched on and off. The data, six nibbles interpreted as a hex number, per LED display comes from $F9, $FA, $FB, for a total of six digits. A bit complicated (see the information below) and hard to emulate without flickering.
    A solution is to patch the SCANDS routine and displaying the hex without the switching off of segments. This works fine for the KIM-1 ROM itself and many programs that call SCANDS to light the LEDs. If the program (many First Book of KIM games e.g.) does bypass SCANDS and go directly to the hardware, it will fail.

Below is a list of, known to me, KIM-1 emulators/simulators. Details below the table.

——————— ————- ————- —————— ——–
Name, website Platform Serial I/O LED display Tape
——————— ————- ————- —————— ——–
KIM-1 Simulator Windows, Linux (Lazarus) terminal builtin SCANDS emulation None
——————— ————- ————- —————— ——–
Linux terminal KIM-1 Emulator Linux CLI CLI SCANDS emulation None
——————— ————- ————- —————— ——–
KIM-1 emulator in JavaScript Web browser No/td> Hardware emulation None
——————— ————- ————- —————— ——–
The Incredible KIMplement C64 Yes Yes ?
——————— ————- ————- —————— ——–
KIM UNO ARDUINO, ESP32, Windows, Linux Yes Yes Yes
——————— ————- ————- —————— ——–

KIM-1 Simulator

My own attempt to KIM-1 emulation. The goal is more to test and study 6502 software for the KIM-1 than cycle exact LED display KIM-1 emulation.
A GUI application. The LED display is simulated by patched SCANDS, so hex digits only, no LED games.
Serial TTY is fully supported including echo suppress and Break detection via the built-in glass teletype console.
Debugging mode allows full access tot the innards of the 6502 or 65C02, the KIM-1. memory view, single/multiple step, run to breakpoint, instruction logging,, cycle counter, disassembly.
Loading and saving to many common formats like MOS papertape, Intel Hex, Motorola S record, binary, hex.
Both RRIOTs, a 6850 ACIA, a LE/switch to the free RRIOT port, RAM to E000, a utility ROM at F000. Runs all known TTY programs.
Things not working yet: LED displays via hardware RRIOT ports (without flickering!), timers in RRIOTs, timed execution to 1 MHz, tape emulation (including the Micro ADE tape motor control support).

Linux KIM-1 emulator

A command line KIM-1 emulator, running on Linux. Runs fine on Raspberry Pi OS.

Simulates LED display with characters displayed at the terminal. Every key entered results in a new line with the LED display. Also supports TTY mode, be it limited to the maximum of 5K RAM in lower memory.
A good attempt to stay close to the bit banging nature of the keyboard entry routine. Limits speed to 1 MHz.

The Incredible KIMplement

A KIM-1 emulator running on a Commodore 64. Which means it will be slow, since 1 MHz 6510 running an emulated 6502, you get the picture. I did test run/Kimplement a long time ago in an C64 emuatator,  The Incredible KIMplement is a KIM-1 emulator for the Commodore 64 (yes, this is not a joke — see the screenshot to the right). It is a true, partial emulation of the original KIM-1 hardware featuring:

  • Powered by “6o6” — a full software NMOS 6502 emulation (documented opcodes only, sorry) with all addressing modes, simulated ROM, and simulated memory-mapped I/O
  • LED and keypad emulation via partial RIOT emulation
  • TTY emulation (ASR-33 subset) via partial RIOT emulation
  • SST emulation
  • 4K RAM expander card
  • KIM-4 emulation with 8K RAM expander card (thus total address space 16K)
  • Revision E ROMs built-in, so you don’t have to find a pirated set download them from your own KIM


The KIM Uno, designed and produced and sold by Oscar Vermeulen, is a very simple “open-source hardware” project that started out as a replica of the classic 1976 KIM-1 computer. Later, Apple-1 compatibility and a 6502 programmable calculator mode were added, plus a built-in ‘early 6502 software gems’ collection.
It costs about $10 in commonly available parts (board & parts without case or power supply), but provides a faithful KIM-1 ‘experience’. An Arduino Pro Mini mounted on the back contains all the logic and memory.

I have two versions: the ‘original’ and the later redesigned version, Software-wise the same, with on the top of the PCB room for power connector (GND, +5V or a 9V battery) and a slide switch. , I use them with an USB cable (the blue one of this page) for power and the serial interface provided.

The software already works on the blue pill STM32 or an ESP32, with manual cabling to the keyboard/display and I expect a new version of the PCB for the ESP32.

The software for the serial interface (you really need a good serial terminal emulator, like Minicom or Tera Term) can be used on any Arduino Uno. After power on  it delivers a simulation of the LED display or the real KIM TTY teletype interface (a bit broken in the current version).

All well described on the pages of Oscar and well worth the money for a ‘6502 SBC’ experience or a Cosmac 1802 with a small LCD.

KIM-1 emulator in JavaScript

By Code Monkey King, web browser based, run it here.

Emulates the keypad/LED display part only. Hardware emulation of LED display. Emulates KIM-1 LED display very well!
Some handy tools like 6502 assembler, paper tape format converter and hexdump generator
No TTY, limited RAM.
Code on github

KIM-1 hardware information relevant to emulation


OVERVIEW OF KIM-1 MEMORY MAP fully extended (A-K connected!)

 0000-1400 RAM
 1600-1700 free, can be RAM or I/O or ROM
 1700-173F I/O and timer of 6530-003
   1700 Port A,
   1701 DDR Port A
   1702 Port B,
   1703 DDR Port B
   1704- timer
 1740-177F I/O and timer of 6530-002, used by  LED/Keyboard/tape
   1740 Port A,
   1741 DDR Port A
   1742 Port B,
   1743 DDR Port B
   1744- timer
 1780-17BF RAM from 6530-003  , free for user applications
 17C0-17FF RAM from 6530-002  , free for user except 0x17E7-0x17FF
 1800-1BFF ROM003
 1C00-1FFF ROM002
    emulator  mirrors last 6 bytes of ROM 002 to FFFB-FFFF:
 2000 - DFFF RAM in simulator

 F000-       ROM in simulator for patching KIM-1 ROM serial I/O and keypad
 FFFA, FFFB - NMI Vector  copy of KIM-1 ROM ROM002
 FFFC, FFFD - RST Vector  copy of KIM-1 ROM ROM002
 FFFE, FFFF - IRQ Vector  copy of KIM-1 ROM ROM002

| ADDRESS |      AREA      | LABEL |              FUNCTION               |
|         |                |       |                                     |
|  00EF   |                | PCL   | Program Counter - Low Order Byte    |
|  00F0   |                | PGH   | Program Counter - High Order Byte   |
|  00F1   |     Machine    | P     | Status Register                     |
|  00F2   |     Register   | SF    | Stack Pointer                       |
|         |     Storage    |       |                                     |
|  00F3   |     Buffer     | A     | Accumulator                         |
|  00F4   |                | Y     | Y-Index Register                    |
|  00F5   |                | X     | X-Index Register                    |
|  1700   |                | PAD   | 6530-003 A Data Register            |
|  1701   |   Application  | PADD  | 6530-003 A Data Direction Register  |
|  1702   |        I/O     | PBD   | 6530-003 B Data Register            |
|  1703   |                | PBDD  | 6530-003 B Data Direction Register  |
|  1704   |                |       | 6530-003 Interval Timer             |
|         | Interval Timer |       |   (See Section 1.6 of               |
|         |                |       |    Hardware Manual)                 |
|  170F   |                |       |                                     |
|  17F5   |                | SAL   | Starting Address - Low Order Byte   |
|  17F6   |   Audio Tape   | SAH   | Starting Address - High Order Byte  |
|  17F7   |   Load & Dump  | EAL   | Ending Address - Low Order Byte     |
|  17F8   |                | EAH   | Ending Address - High Order Byte    |
|  17F9   |                | ID    | File Identification Number          |
|  l7FA   |                | NMIL  | NMI Vector - Low Order Byte         |
|  l7FB   |                | NMIH  | NMI Vector - High Order Byte        |
|  l7FC   |   Interrupt    | RSTL  | RST Vector - Low Order Byte         |
|         |    Vectors     |       |                                     |
|  17FD   |                | RSTH  | RST Vector - High Order Byte        |
|  l7FE   |                | IRQL  | IRQ Vector - Low Order Byte         |
|  17FF   |                | IRQH  | IRQ Vector - High Order Byte        |
|  1800   |                | DUMPT | Start Address - Audio Tape Dump     |
|         |  Audio Tape    |       |                                     |
|  1873   |                | LOADT | Start Address - Audio Tape Load     |
|  1C00   | STOP Key + SST |       | Start Address for NMI using KIM     |
|         |                |       | "Save Nachine" Routine (Load in     |
|         |                |       | 17FA & 17FB)                        |
|  17F7   |   Paper Tape   | EAL   | Ending Address - Low Order Byte     |
|  17F8   |    Dump (Q)    | EAH   | Ending Address - High Order Byte    |

KIM-1 hardware


PB0 TTY data out (can block  hardware TTY echo)
PB1 - PB4 outputs led select via 74145 6 leds O4 -O9 on/off, keypad O0-O3
PB5 TTY/audio control (block/allow inputs)
    can block TTY input and audio input
PB7 audio in/out

PA0-6 keypad + LED segments
PA7 TTY data in


PB1 - PB4 to ABCD inputs
O4 to O9 LED on U18 to U23

O0 to O3 to key rows 

PB   PB1 PB2 PB3 PB4                   													  
     A   B   C   D 
00-01   0   0   0   0  00 O0 keyrow 0      
02-03   1   0   0   0  01 O1        1     
04-05   0   1   0   0  02 O2        2 
06-07   1   1   0   0  03 O3        3

08-09   0   0   1   0  O4 LED enable U18
0A-0B   1   0   1   0  O5            U19
0C-0D   0   1   1   0  O6            U20
0E-OF   1   1   1   0  O7            U21
10-11   0   0   0   1  O8            U22
12-13   1   0   0   1  o9            U23		

 750  1E8C  A2 00     INIT1   LDX   #$00      
 751  1E8E  8E 41 17          STX   PADD      FOR SIGMA USE SADD	
PAx is input

 752  1E91  A2 3F             LDX   #$3F
 753  1E93  8E 43 17          STX   PBDD      FOR SIGMA USE SBDD
3F = 00111111
PB0 - PB5 output, PB7 input

 754  1E96  A2 07             LDX   #$07      ENABLE DATA IN
 755  1E98  8E 42 17          STX   SBD       OUTPUT
PB0 = 1 high TTY, stopbit
PB1 -PB2 high (keypad?)

PB5 low ; allow input
PB7 low : audio quiet


toggle PB0 via read SBD, AND $FE, OR $01 and write SBD, end with 1 


              ;          CONDITION OF SSW KEY NOT DEPRESSED OR
 805                  ;          TTY MODE  A=0
 806                  ;          KEY DEPRESSED OR KB MODE  A NOT ZERO
 807  1EFE  A0 03     AK      LDY   #$03      3 ROWS
 808  1F00  A2 01             LDX   #$01      DIGIT 0
 809  1F02  A9 FF     ONEKEY  LDA   #$FF
 810  1F04  8E 42 17  AK1     STX   SBD       OUTPUT DIGIT
via 74145 Start with digit 0, continue with next row 

 811  1F07  E8                INX             GET NEXT DIGIT
 812  1F08  E8                INX 
 813  1F09  2D 40 17          AND   SAD       INPUT SEGMENTS
and key pressed to A	

 814  1F0C  88                DEY 
 815  1F0D  D0 F5             BNE   AK1

 816  1F0F  A0 07             LDY   #$07
 817  1F11  8C 42 17          STY   SBD
back to INITS state

 818  1F14  09 80             ORA   #$80
 819  1F16  49 FF             EOR   #$FF
set high bit and inverse all
A=0 no key

 820  1F18  60                RTS 

 822  1F19  A0 00     SCAND   LDY   #$00      GET DATA                      1F19
 823  1F1B  B1 FA             LDA   (POINTL),Y  SPECIFIED BY POINT
 824  1F1D  85 F9             STA   INH       SET UP DISPLAY BUFFER

 825  1F1F  A9 7F             LDA   #$7F      CHANGE SEG
 826  1F21  8D 41 17          STA   PADD      TO OUTPUT

PA0 - PA6 output

 827  1F24  A2 09             LDX   #$09      INIT DIGIT NUMBER start with U18
 828  1F26  A0 03             LDY   #$03      OUTPUT 3 BYTES 6 hex numbers
 829  1F28  B9 F8 00  SCAND1  LDA   INL,Y     GET BYTE
 830  1F2B  4A                LSR   A         GET MSD high byte
 831  1F2C  4A                LSR   A
 832  1F2D  4A                LSR   A
 833  1F2E  4A                LSR   A
 834  1F2F  20 48 1F          JSR   CONVD     OUTPUT CHAR
 835  1F32  B9 F8 00          LDA   INL,Y     GET BYTE AGAIN
 836  1F35  29 0F             AND   #$0F      GET LSD low byte
 837  1F37  20 48 1F          JSR   CONVD     OUTPUT CHAR
 838  1F3A  88                DEY             SET UP FOR NEXT BYTE
 839  1F3B  D0 EB             BNE   SCAND1
 840  1F3D  8E 42 17          STX   SBD       ALL DIGITS OFF 
X = 0?

 841  1F40  A9 00             LDA   #$00      CHANGE SEGMENT
 842  1F42  8D 41 17          STA   PADD      TO INPUTS
PA0-PA7 inputs

 843  1F45  4C FE 1E          JMP   AK        GET ANY KEY

 844                  ;       ** CONVERT AND DISPLAY HEX (USED BY SCAND ONLY)**
show character on LED 

 845  1F48  84 FC     CONVD   STY   TEMP
 846  1F4A  A8                TAY             SAVE Y
 847  1F4B  B9 E7 1F          LDA   TABLE,Y   USE CHAR AS INDEX
 848  1F4E  A0 00             LDY   #$00      LOOKUP CONVERSION
 849  1F50  8C 40 17          STY   SAD       TURN OFF SEGMENTS
PA0-PA7 0 

 850  1F53  8E 42 17          STX   SBD       OUTPUT DIGIT ENABLE
X = LED number U18-U23 decimal  to 74145

 851  1F56  8D 40 17          STA   SAD       OUTPUT SEGMENTS
write segment from table to LED

 852  1F59  A0 7F             LDY   #$7F      DELAY 500 CYCLES
 853  1F5B  88        CONVD1  DEY   
 854  1F5C  D0 FD             BNE   CONVD1
 855  1F5E  E8                INX             GET NEXT DIGIT NUMBER
 856  1F5F  E8                INX             ADD 2
 857  1F60  A4 FC             LDY   TEMP      RESTORE Y
 858  1F62  60                RTS

GETKEY > 15 ? no key
14 = PC
10 = addressmode
11 - Datamode
12 = step
13 = RUN
0 - F - hex digit

/* RIOT2 explanation: better emulation of LED display through simulated hardware rather than 2014's ROM patch
 *  The RIOT-002 chip is used to drive the LEDs, read the keypad, and control TTY and tape.
 *  KIM Uno only emulates the LED driver and timer hardware; the keypad, TTY and tape are emulated on a higher abstraction level in the ROM
 *  On the real KIM-1, the keyboard columns are PA0-PA6 and the rows are selected through 
 *                     the display  columns are PA0-PA6 and the segment led is decoded from PB 0000 1110
 *                     teletype mode is detected when  = 1.
 *                     teletype uses PB0, PB5, PA7
 *  1740 Data port A            Selects pattern to show on a segment LED (PA0-6) and TTY (PA7)
 *  1741 Data Direction port A  Are the GPIO pins set to input or output?
 *  1742 Data port B            Selects which of the 6 segment LEDs is lit up (PB1-3), 
 *                              and also: PB0 (TTY), PB4 ???, PB5 (TTY/tape input?), PB 6(RIOT internal, ChipSelect), PB7 (tape output)
 *  1743 Data direction port B  Are the GPIO pins set to input or output?

void write1740(void)            // ======== PA pins - set the individual LED segments on or off
  //riot2regs.ioPAD &= 0x7F;    // only the bits for the 7 LEDs in a segment LED
  for (uint8_t ibit=0; ibit<7; ibit++) 
      digitalWrite(kCols[ibit], (riot2regs.ioPAD & (1<<ibit))==0);       // set the bit, inverted through ==0

void write1741(void)            // ======== Data direction register for PA
  for (uint8_t ibit=0; ibit<7; ibit++) 
    if ( riot2regs.ioPADD & (1<<ibit) )
      pinMode(kCols[ibit], OUTPUT);           // set pin to output
      pinMode(kCols[ibit], INPUT);           // set pin to output

void write1742(void)            // ======== PB pins - set which of the 6 segment LEDs is lit up
  uint8_t led = ((riot2regs.ioPBD - 9) >> 1) & 0b111; // identify the selected segment LED

  for (uint8_t iLed=0;iLed<6;iLed++)       // set GPIO pins of all 6 KIM-1 LED segments
  { if (iLed==led)    
      digitalWrite(ledSelect[iLed], HIGH); // power up this segment LED
      digitalWrite(ledSelect[iLed], LOW);  // power down the other segment LEDs

void write1743(void)            // ======== Data direction register for PB
  // TEMP: all LED pins are set to output; there's no functionality we need except that.
  for (uint8_t iLed=0;iLed<6;iLed++)
    pinMode(ledSelect[iLed], OUTPUT);  
} // end of C segment


Found in Hobbycomputer #1 (c) 1980 Herwig Feichtinger (of EMUF fame!) improved by Nils Andreas, a phonebook
In fact, it is a searchable text database. Full article here

The program is written, probably by hand, Herwig Feichtinger in the German magazine Hobbycomputer, Issue 1.

On the github page of Nils you can find source and executables.

Hobby Computer magazine

A German magazine, from Franzis Verlag. Sonderheft der ELO Funkschau Elektronik

Full magazines at Here you will find the articles of interest about KIM-1 and 6502.

Hobbycomputer 1

KIM-1 articles llike Telefonbuch. See also the page on Telefonbuch restauration.







Hobbycomputer 2

KIM-1 and more general 6502 articles.