elficpu2

This is a simple 8-bit CPU written in VHDL and an improvement of my elficpu1.

Features

• 8-bit CPU
• Up to 65536 bytes of instruction memory
• Up to 65536 bytes of data memory
• Up to 65536 I/O ports
• Two general purpose registers R0 and R1
• One 32-bit counter register CNT
• One 16-bit STACK register

Reset behaviour

All registers are set to 0.

Instructions

• nop. No operation :)
• R0 = const. Load register R0 with a 8-bit constant data. Opcode: 1h XX.
• R1 = const. Load register R1 with a 8-bit constant data. Opcode: 2h XX.
• halt. Halts CPU. Opcode: FFh.
• portaddr = R0. Write register R0 to port. Opcode: 3h, XX, YY.
• portaddr = R1. Write register R1 to port. Opcode: 4h, XX, YY.
• CNT = const. Load register CNT with a 32-bit constant value. Opcode: 5h, AA, BB, CC, DD
• --CNT. Decrement CNT register. Opcode: 6h.
• jumpnz(addr). Jump on CNT register is not zero. Opcode: 7h, AA, BB, CC, DD.
• jump(addr). Jump to address. Opcode: 7h, AA, BB, CC, DD.