Questions tagged [io]

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5
votes
1answer
155 views

Why is my program outputting only zeros to data bus during IO operations?

I'm building a breadboard Z80 based computer. As now, I have the CPU hooked up to an eeprom and an IO device (an HD44780 character display) with appropriate decoding logic. The rom chip starts at ...
2
votes
1answer
119 views

READY / WAIT when reading from / writing to IO ports

During the execution of an IN or OUT instruction (so after the opcode and its single-byte argument have been fetched from memory), how does the Intel 8080 react to its READY pin going down? Is it ...
7
votes
2answers
1k views

Did general purpose I/O controller chips come with fewer than 40 pins?

I'm aware that 40-pins was a high-water mark for dual-inline package chips for a significant time; many CPUs of the early 1980s (8086, Z80, 6800, 6502, etc) used 40-pin packages, but no larger. ...
15
votes
1answer
836 views

Why did POKEing ROM addresses mask port writes?

After reading mcleod_ideafix's answer about the Inves Spectrum+'s "randomize of death", specifically his article on the subject, one thing struck me as odd. From César Hernández Bañó's research: ......