IA6805E2 29 August 2007
Microprocessor Unit
As of Production Version 00
Instruction Set Description
The MPU has 61 basic instructions divided into 5 types. The 5 types are Register/memory, read-
modify-write, branch, bit manipulation, and control.
Register/Memory Instructions:
Most of the following instructions use two operands. One is either the accumulator or the
index register and the other is obtained from memory. The jump unconditional (JMP) and
jump to subroutine (JSR) instructions have no register operand.
Function Mnemonic
Load A from memory LDA
Load X from memory LDX
Store A in memory STA
Store X in memory STX
Add memory to A ADD
Add memory and carry to A ADC
Subtract memory SUB
Subtract memory from A with Borrow SBC
AND memory to A AND
OR memory with A ORA
Exclusive OR memory with A EOR
Arithmetic compare A with memory CMP
Arithmetic compare X with memory CPX
Bit test memory with A (logical compare) BIT
Jump Unconditional JMP
Jump to subroutine JSR
Read-Modify-Write Instructions:
These instructions read a memory or register location, modify or test its contents and then
write the modified value back to memory or the register.
Function Mnemonic
Increment INC
Decrement DEC
Clear CLR
Complement COM
Negate (2's complement) NEG
Rotate Left Thru Carry ROL
Rotate Right Thru Carry ROR
Logical shift left LSL
Logical shift right LSR
Arithmetic shift right ASR
Test for negative or zero TST
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