The board is useful to verify that you have the address and databus working to some degree and that connections to the ROM and GLUE are also good enough to complete the first few bus cycles of the system. You can select up to 64 addresses with data to verify GLUE and ROM and other parts of the system have the correct levels by using a scope or meter. It also verifies the reset signal and 8MHz clock is working via 2 LEDs.
This will hardwire the address bus so you can check the first few ROM addresses which are configurable by jumper links. When closed they are "0" and when open they are "1".
To use, simply remove the 68K CPU from your motherboard and plug this bus diagnostics board in instead. During reset all the low LEDs will be late indicating all zeros. After reset, see the patterns as illustrated below, assuming you are using TOS104.
The data is shown on a bank of LEDs. HI and LO LEDs will light up.
It also will light 2 LEDs if the 8MHz clock is working on the far left of the board. Both LEDs must be lite. They are triggered on the HI and LO of the clock.
Assuming you have all the jumper links closed, this sets address to $FC0000.
In a HEX editor as illustrated above, you can see the very first bytes in TOS1.04 are $2E60. These need needs to be flipped to $602E which is %0110000000101110
The arrangement of the databits on the CPU bus is DATA
15..0. So the binary number becomes as illustrated on the LEDs in the
image below.
So now you know what the expected voltages are on each data line, you can test those voltages across the motherboard at various locations such as ROM,GLUE,MMU etc.
If for example somewhere you had a short between D15 and D14 ( using the above image as reference) then both data lines show "low". In this case you know you have a short circuit between those two data lines than can investigate those traces to see whether possible short-circuit is.
Another useful tool is a low resistance meter as illustrated in THIS thread. This can give a "direction" to where the short is originating from going by minute resistance differences across the motherboard traces.
(A7,A6,A5,A4,A3,A2) - (HEX SWAPPED) - (D15...D0)
000000 - $602E - %0110000000101110
000001 - $00FC - %0000000011111100
000010 - $00FC - %0000000011111100
000011 - $0000 - %0000000000000000
000100 - $00FC - %0000000011111100
000101 - $00FE - %0000000011111110
000110 - $0406 - %0000010000000110
000111 - $0007 - %0000000000000111
001000 - $0000 - %0000000000000000
001001 - $0000 - %0000000000000000
001010 - $0000 - %0000000000000000
001011 - $0000 - %0000000000000000
001100 - $46FC - %0100011011111100
001101 - $4E70 - %0100111001110000
001110 - $0CB9 - %0000110010111001
001111 - $235F - %0010001101011111
010000 - $0000 - %0000000000000000
010001 - $4DFA - %0100110111111010
010010 - $4EF9 - %0100111011111001
010011 - $0004 - %0000000000000100
010100 - $0006 - %0000000000000110
010101 - $0616 - %0000011000010110
010110 - $1B6D - %0001101101101101
010111 - $8001 - %1000000000000001
011000 - $3141 - %0011000101000001
011001 - $0426 - %0000010000100110
011010 - $202D - %0010000000101101
011011 - $4A2D - %0100101000101101
011100 - $660E - %0110011000001110
011101 - $0000 - %0000000000000000
011110 - $2040 - %0010000001000000
011111 - $FFE2 - %1111111111100010
100000 - $9BCD - %1001101111001101
100001 - $8800 - %1000100000000000
100010 - $0007 - %0000000000000111
100011 - $00C0 - %0000000011000000
100100 - $10BC - %0001000010111100
100101 - $117C - %0001000101111100
100110 - $0002 - %0000000000000010
100111 - $0000 - %0000000000000000
101000 - $670E - %0110011100001110
101001 - $0006 - %0000000000000110
101010 - $0D1A - %0000110100011010
101011 - $0002 - %0000000000000010
101100 - $43ED - %0100001111101101
101101 - $303C - %0011000000111100
101110 - $41FA - %0100000111111010
101111 - $32D8 - %0011001011011000
110000 - $FFFC - %1111111111111100
110001 - $0001 - %0000000000000001
110010 - $422D - %0100001000101101
110011 - $1C2D - %0001110000101101
110100 - $2A2D - %0010101000101101
110101 - $4DFA - %0100110111111010
110110 - $6000 - %0110000000000000
110111 - $6700 - %0110011100000000
111000 - $4246 - %0100001001000110
111001 - $000A - %0000000000001010
111010 - $307C - %0011000001111100
111011 - $43F9 - %0100001111111001
111100 - $0008 - %0000000000001000
111101 - $30C0 - %0011000011000000
111110 - $D07C - %1101000001111100
111111 - $B1FC - %1011000111111100
If you need other by sequences you can try our tool HERE. Note that hotlinking to this page is not allowed.
The board requires minimal assembly. Solder the round header pins as illustrated in the above images. Technically you don't need the single pin on its own as it is a second VCC input. Solder the square pins for the jumpers and a small modification to solder blob 2 points. Then your ready to go!