Atari Signature Analysis Service Manual

 1How Atari Signature Analysis Works 
Written by Phillip Eaton - [email protected]   
*Comments and feedback welcome & appreciated* 
 
Revision 1.1 – 2001-09-20 
· Updated contact links 
· Minor text changes 
Revision 1.0 - 1999-12-26 
· Initial Release 
 
Introduction 
Ever wondered what all those 4-digit ‘signatures’ are, that are dotted around the Atari circuit 
diagrams? They are used for diagnosing game PCB faults with an Atari CAT Box. They are 
useful because, armed with a CAT Box and a game...

 2Basically, the CAT Box has it’s own processor which then can control the game PCB address & 
data bus, using the PCB’s clock signal. It can then be used to address individual areas of the 
board for checking individual components, using the knobs and switches on the CAT Box 
control panel. 
So now you know what a CAT Box is, you have a problem – you don’t have one. So why should 
you bother reading any further? Well, you might want to read on because you’re interested, 
but there are other reasons....

 3 
Figure 2 CAT Box Counter Circuitry 
This is implemented by four cascaded 4-bit counters on two 74LS393 ICs. The 74LS244 ICs 
are used as buffers onto the address bus. (Note there appears to be a bug in the Atari diagram 
– the second counter on IC B5 appears to be cascading itself! If you understand the diagram, 
you should be able to spot the easy fix.) 
Why is discrete hardware used to cycle round the address bus, when the CAT Box has its own 
6502 processor, and can address all of the PCBs address...

 4 
Figure 3 Start, Stop and Clock Probes  

 5    
Figure 4 Data Probe 
Consider the case where you want to check the signature of a ROM that is still plugged into the 
PCB. This IC will occupy a certain position in the address space of the PCB. When the 16-bit 
address counter cycles through the address space, for a period, the ROM will be enabled and 
then disabled. This will happen once per cycle of the counter.  
When testing the signature, you would connect:  
· Start and Stop probes to the Chip Enable line of the ROM.  
· Clock probe to the...

 6 
Figure 5 Signature Loop 
The data held in the shift register(s) is fed back through XOR gates together with the SRDATA 
signal to create a new piece of data that is then shifted in to form a new signature. 
At the end of each cycle (I guess) the processor reads the SIG0 to SIG15 lines which form a 
16-bit (four hex digit) signature, and updates the seven-segment display on the CAT Box 
control panel. Then, the SIG RST line would be used to reset the LS193 counter. 
Signature Analysis Emulator 
To...

 7 
Table 1 Signature Analysis Emulation Program 
 
 Atari Signal Analysis for ROM Images Emulator Program 
 
 Written using Microsoft MS-DOS QBasic Version 1.1 
 
 Written by Phillip Eaton 1999-12-18 
            mailto:[email protected] 
            http://www.pjeaton.demon.co.uk 
            *Comments and feedback welcome & appreciated* 
 
 Program Description: 
   Uses software emulation of Cyclic Redundancy Check method as implemented 
   in Atari CATBOX hardware for checking integrity of...

 8 
 
 AtariHEX$ 
 Description:  Recursive procedure to convert an ASCII representation of a 
               hex number to Atari Sig Analysis format, where B,C,D,E,F are 
               replaced by C,F,H,P,U. 
 Parameters:   Crc$ - ASCII representation of a hex number 
 Returns:      Crc$ with [BCDEF] characters changed to [CFHPU] 
 
 
FUNCTION AtariHEX$ (Crc$) 
 
 Operation of this function is an exercise for the reader! 
IF Crc$ =  THEN 
AtariHEX$ = Crc$ 
ELSE 
SELECT CASE LEFT$(Crc$, 1) 
CASE IS = B...

 9 
Figure 6 Centipede Signatures 
Most of the circuit diagrams for Atari Games have signatures marked on them, but these are 
usually just logic circuitry signatures, not for the ROM’s. I guess this is so the circuit diagrams 
were not software dependent, which allowed them to modify the software without invalidating 
the circuit diagrams that were already released. You’ll need to get your hands on the actual 
Signature Analysis Guides (or at least the signatures) to check your test results. 
Atari...

 10Atari also produced some ‘pods’ which allowed the CAT Box’s 6502 to control Z80 and other 
processor-based hardware. These were simple passive devices that were used to modify the 
read/write control line format. This differs slightly between the different types of processor 
used at the time. 
My Dig Dug board, which has 3 Z80 processors, doesn’t even have the 50-way connector, so 
the CAT Box needs to be connected through the processor socket. 
If you wanted to use it on a non-Atari PCB, you would...