Pep/9
![Pep/9 CPU and memory](/assets/second-brain/2020-10-07-16-54-37.png)
![Pep/9 instruction format](/assets/second-brain/2020-10-09-10-37-34.png)
- Either 1 byte or 3 bytes in length
- 1 byte --> operand specifier not included
- 3 bytes --> operand specifier included
- Two parts
- 8-bit instruction specifier
- 16-bit operand specifier
Instruction Specifier
- Op codes vary from 4 bits to 8 bits long
- 5th bit is the register specifier
- 3-bit addressing mode specifier
- Indicates hot to interpret contents of operand specifier
- Address mode $000$ --> operand specifier contains data value to be used as operand
- Address mode $001$ --> operand specifier contains memory address
Computer Science Computing Systems