ST72F324BJ STMICROELECTRONICS [STMicroelectronics], ST72F324BJ Datasheet - Page 133

• Manufacturer Part Number: ST72F324BJ
• Description: 8-bit MCU, 3.8 to 5.5 V operating range with 8 to 32 Kbyte Flash/ROM, 10-bit ADC, 4 timers, SPI, SCI
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

ST72324B
Using a prebyte
The instructions are described with one to four opcodes.
In order to extend the number of available opcodes for an 8-bit CPU (256 opcodes), three
different prebyte opcodes are defined. These prebytes modify the meaning of the instruction
they precede.
The whole instruction becomes:
PC-2
PC-1
PC
PC+1
These prebytes enable the instruction in Y as well as indirect addressing modes to be
implemented. They precede the opcode of the instruction in X or the instruction using direct
addressing mode. The prebytes are:
PDY 90
PIX 92
PIY 91
Replace an X based instruction using immediate, direct, indexed, or inherent
End of previous instruction
Prebyte
Opcode
Replace an instruction using direct, direct bit, or direct relative addressing mode
Replace an instruction using X indirect indexed addressing mode by a Y one.
effective address
to an instruction using the corresponding indirect addressing mode.
It also changes an instruction using X indexed addressing mode to an instruction
using indirect X indexed addressing mode.
Additional word (0 to 2) according to the number of bytes required to compute the
addressing mode by a Y one.
Instruction set
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