The DAC is the Burr Brown DAC7644, it has the capability to read back what is in the DAC's data register. It also has the capability to hold the digital data as it is entered, and only transfer it to the actual D/A converters on a strobe signal given later.
These are the addresses on the board : Addr Function 0 chan 0 low byte 1 chan 0 high byte 2 chan 1 low byte 3 chan 1 high byte 4 chan 2 low byte 5 chan 2 high byte 6 chan 3 low byte 7 chan 3 high byte 8 write anything loads data into dac 9 - 11 no function 12 select Load DAC mode 13, 14 not used 15 Module ID code 0x21If a 0 is written to reg 12, then the loading of data to the DAC is controlled by a pulse on the INTR EPP bus line. This is intended to be generated by the timer on the master encoder board. If a 1 is written to that register, then the loading of data to the DAC is commanded by writing anything to reg 8. This is conveniently set up so that it can be written right after writing the last data byte to reg 7.
As on the encoder board, the first register to be addressed is written with an ADDRSTB signal with the address of the board and desired register on the data lines. Then, registers can be read or written sequentially by pulses on the DATASTB line.
The data format is as follows : +10 V output 0xFFFF 0 V 0x8000 -10 V 0x0000