It is the interface circuit between AD574 and printer.

It is the interface circuit between AD574 and printer . The computer 's printing interface has two write registers, one is a data register with an address
of 3BCH, and the other is a command register with an address of 3BEH. There are also three read registers: the read data register at address 3BCH,
the read status register at address 3BDH, and the read command register at address 3BEH. As can be seen from the figure, AD574 is hung on the printer interface
. First, OFFH is written into the data register (3BCH) of the printer interface through software programming. Make pins 2 to 9 on the DB25 pin
a positive pull-up level} Secondly, start the A/D in reduced range, first write 03H to the command register of the printer interface, so that the cs and R/ C on AD
5 74 and AO are both low level, starting 12-bit/VD, and then writing 04H to this register. Disable cs, R/C and AO; again,
judge whether the AlD conversion is completed by reading the status register (3BDH). When D3 -1, A/D conversion is in progress. When D3-0,
the A/D conversion has ended; finally, the A/D conversion result is read into the computer . .