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!

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.


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.







Update to the KIM-1 Simulator

Nils, a very enthousiast PAL-1 user discovered in an old German magazine, 1979, HobbyComputer 1, a small phonebook program for the KIM-1.
It is a command line utility, extremely small and quite clever. See the post about it here.

So he entered the code in assembler and did some tests on his PAL-1 (it worked) and in the KIM-1 Simulator, which was not working.
He found the ‘database’ corrupted.

Of course I had to look at it and see what was going on. It had to be something about using zeropage pointers into the database.
And it was. In the source an instruction appeared:

INY  ; Y = 0

followed by an indirect addressing, Y into the database and preceded by a call to getch, reading a character from the keyboard.
Y was not used in the program before, so in the Simulator it was uncertain what the value was.

GETCH is known to destroy the Y register, delivering the character in register A. How is unspecified.
In the KIM-1 Simulator the KIM-1 GETCH is patched to the ACIA routines of the emulated 6850 serial interface.
Those routines do not use Y, so it is left untouched.

So time to study the KIM-1 routines. In the delay a bit routine the Y register is filled with the final state of a counter, TIMH.
It looks like the decrement ends with the value $FF, when the BPL becomes false, the whole purpose of the use of Y seems to determine that end of the loop?

 1ED4  AD F3 17  DELAY   LDA   CNTH30                           
 1ED7  8D F4 17          STA   TIMH
 1EDA  AD F2 17          LDA   CNTL30
 1EDD  38        DE2     SEC   
 1EDE  E9 01     DE4     SBC   #$01 
 1EE0  B0 03             BCS   DE3  
 1EE2  CE F4 17          DEC   TIMH
 1EE5  AC F4 17  DE3     LDY   TIMH
 1EE8  10 F3             BPL   DE2
 1EEA  60                RTS

Anyway, the KIM-1 Simulator 0.9.4. GETCH routine now returns with Y=$FF and the phonebook program seems to work.

DOS/65 sources

Different versions (from 2008 to 2021) of this CP/M for the 6502 system by Richard Leary hosted here.

Work in progress, hope to get more information from Richard!

with his permission

KIM-1 Diagnostic board

Dwight Elvey designed and programmed a diagnostic board for the KIM-1, to determine what might be wrong with the KIM-1
The board switches off the 6530 ROMs and one can run tests on teh onboard ROM, looking for for defective RAM, defective LED display, defective 6530 ports.

Here I present the complete design of the board, with help and permission of Dwight Elvey, Santo Nucifora and Liu Ganning.