Datasheet

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ST7LITE20F2 ST7LITE25F2 ST7LITE29F2 Instruction set
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Using a prebyte
The instructions are described with 1 to 4 bytes.
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: End of previous instruction
• PC-1: Prebyte
• PC: Opcode
• PC+1: Additional word (0 to 2) according to the number of bytes required to compute
the effective address.
These prebytes enable 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: Replace an X based instruction using immediate, direct, indexed, or inherent
addressing mode by a Y one.
• PIX 92: Replace 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.
• PIY 91: Replace an instruction using X indirect indexed addressing mode by a Y one.
12.2.1 Illegal opcode reset
In order to provide enhanced robustness to the device against unexpected behavior, a
system of illegal opcode detection is implemented. If a code to be executed does not
correspond to any opcode or prebyte value, a reset is generated. This, combined with the
Watchdog, allows the detection and recovery from an unexpected fault or interference.
Note: A valid prebyte associated with a valid opcode forming an unauthorized combination does
not generate a reset.
Bit operation BSET BRES −−− − −−
Conditional Bit Test and Branch BTJT BTJF −−− − −−
Arithmetic operations ADC ADD SUB SBC MUL −−−
Shift and Rotates SLL SRL SRA RLC RRC SWAP SLA −
Unconditional Jump or Call JRA JRT JRF JP CALL CALLR NOP RET
Conditional Branch JRxx −−−− −−−
Interruption management TRAP WFI HALT IRET −−−−
Condition Code Flag modification SIM RIM SCF RCF −−−−
Table 55. Instruction groups (continued)
Group Instructions