PM0044 datasheet(62/162 Pages) STMICROELECTRONICS

62 / 162 page

STM8 instruction set

PM0044

62/162

Doc ID 13590 Rev 3

Using a pre-code (two-byte op-codes)

In order to extend the number of available op-codes for an 8-bit CPU (256 op-codes), four

different pre-code bytes are defined. These pre-codes modify the meaning of the instruction

they precede.

The whole instruction becomes:

These pre-bytes are:

PC-1

End of previous instruction

Pre-code

PC+1

Op-code

PC+2

Additional word (0 to 3) according to the number of bytes required to compute the

effective address

0x90 = PDY

Replaces an X based instruction using immediate, direct, indexed or

inherent addressing mode by a Y one.

It also provides read/modify/write instructions using Y indexed

addressing mode with long offset and two bit handling instructions

(BCPL and BCCM)

0x92 = PIX

Replaces an instruction using direct, direct bit, or direct relative

addressing mode 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.

0x91 = PIY

Replace an instruction using indirect X indexed addressing mode by

a Y one.

0x72 = PWSP

Provide long addressing mode for bit handling and read/modify/write

instructions.

It also provides indirect addressing mode with two byte pointer for

read/modify/write and register/memory instructions.

Finally it provides stack pointer indexed addressing mode on

PM0044 데이터시트(PDF) 62 Page - STMicroelectronics