Implement BEOR instruction #92
Description
Implement the BEOR 6309 instruction mnemonic in the assembler. Logically XORs the specified bit in the A, B, or CC with a bit in memory. Result is stored in the source register. Direct addressing mode only. The first two bytes of the instruction are the instruction code, the next byte is a postbyte, and the last byte is the address least significant byte.
Direct - $1134, 4 bytes
Example:
BEOR B,2,4,$40
The above would XOR bit 4 of B with bit 2 of DP:40, storing the result in B. Note the strange order here - following B you specify the bit in the memory location, followed by the bit in the register. The resulting machine code would be:
11 34 A2 40
The postbyte is composed of the following sections:
- Bits 7-6: register code where 00 =
CC, 01 =A, 10 =B, 11 = invalid - Bits 5-3: the bit number (0-7) in memory
- Bits 2-0: the bit number (0-7) in the register