Intel 8080 Instruction at OP Code 0x20 and 0x30

Question

According to Intel's 8080-8085 Assembly Language Programming guide, the OP Code 20 corresponds to the Read Interrupt Mask (RIM) instruction, and 30 corresponds to the Set Interrupt Mask (SIM) instruction.

However, only the 8085 has the RST5.5, RST6.5, and RST7.5 hardware interrupts. Are the instructions at 0x20 and 0x30 just NOP on 8080 hardware?

I assume it still has the masking register, so you could read back what you have written. Try it? :) — Jester
According to this 0x20 and 0x30 on the 8080 are treated as NOPs : pastraiser.com/cpu/i8080/i8080_opcodes.html — Michael Petch

Tommylee2k Tommylee2k · Accepted Answer · 2016-03-29T16:57:35

The 8085 has 2 instruction functions:

To read and set the interrupt mask.
To communicate via serial port interface.

On 8080, these opcodes are NOPs.

Intel 8080 Instruction at OP Code 0x20 and 0x30

1 Answers