Instruction format

Every opcode is 16 bits wide (0xABCD):

• A — instruction group.
• B — sub-opcode or register nibble.
• C — usually a register or the upper 4 bits of an address.
• D — usually a register or the lower 4 bits of an address.

Example, ADD R0, R1 encodes as 0x1101:

0001 0001 0000 0001

Jump/load/store instructions treat XXX in 0xYXXX as a 12-bit address, covering the full 4 KiB memory bank.