MC912DG128A Motorola, MC912DG128A Datasheet - Page 26

• Manufacturer Part Number: MC912DG128A
• Description: Microcontrollers
• Manufacturer: Motorola

Opcodes and Operands
Central Processing Unit
MC68HC912DT128A Rev 2.0
26
The CPU12 uses 8-bit opcodes. Each opcode identifies a particular
instruction and associated addressing mode to the CPU. Several
opcodes are required to provide each instruction with a range of
addressing capabilities.
Only 256 opcodes would be available if the range of values were
restricted to the number that can be represented by 8-bit binary
numbers. To expand the number of opcodes, a second page is added to
the opcode map. Opcodes on the second page are preceded by an
additional byte with the value $18.
To provide additional addressing flexibility, opcodes can also be
followed by a postbyte or extension bytes. Postbytes implement certain
forms of indexed addressing, transfers, exchanges, and loop primitives.
Extension bytes contain additional program information such as
addresses, offsets, and immediate data.
Central Processing Unit
MOTOROLA
6-cpu12