SAB80515 Datasheet, PDF (133/270 Pages) Siemens Semiconductor Group – 8-Bit Single-Chip Microcontroller Family

Instruction Set
Unconditional Calls, Returns and Jumps
Unconditional calls, returns and jumps transfer control from the current value of the program
counter to the target address. Both direct and indirect transfers are supported.
– ACALL and LCALL push the address of the next instruction onto the stack and then transfer
control to the target address. ACALL is a 2-byte instruction used when the target address is
in the current 2K page. LCALL is a 3-byte instruction that addresses the full 64K program
space. In ACALL, immediate data (i.e. an 11-bit address field) is concatenated to the five most
significant bits of the PC (which is pointing to the next instruction). If ACALL is in the last 2
bytes of a 2K page then the call will be made to the next page since the PC will have been
incremented to the next instruction prior to execution.
– RET transfers control to the return address saved on the stack by a previous call operation
and decrements the SP register by two (2) to adjust the SP for the popped address.
– AJMP, LJMP and SJMP transfer control to the target operand. The operation of AJMP and
LJMP are analogous to ACALL and LCALL. The SJMP (short jump) instruction provides for
transfers within a 256-byte range centered about the starting address of the next instruction
(– 128 to + 127).
– JMP @A + DPTR performs a jump relative to the DPTR register. The operand in A is used as
the offset (0 - 255) to the address in the DPTR register. Thus, the effective destination for a
jump can be anywhere in the program memory space.
Conditional Jumps
Conditional jumps perform a jump contingent upon a specific condition. The destination will be
within a 256-byte range centered about the starting address of the next instruction (– 128 to + 127).
– JZ performs a jump if the accumulator is zero.
– JNZ performs a jump if the accumulator is not zero.
– JC performs a jump if the carry flag is set.
– JNC performs a jump if the carry flag is not set.
– JB performs a jump if the directly addressed bit is set.
– JNB performs a jump if the directly addressed bit is not set.
– JBC performs a jump if the directly addressed bit is set and then clears the directly addressed
bit.
– CJNE compares the first operand to the second operand and performs a jump if they are not
equal. CY is set if the first operand is less than the second operand; otherwise it is cleared.
Comparisons can be made between A and directly addressable bytes in internal data memory
or an immediate value and either A, a register in the selected register bank, or a register
indirectly addressable byte of the internal RAM.
– DJNZ decrements the source operand and returns the result to the operand. A jump is
performed if the result is not zero. The source operand of the DJNZ instruction may be any
directly addressable byte in the internal data memory. Either direct or register addressing may
be used to address the source operand.
Interrupt Returns
– RETI transfers control as RET does, but additionally enables interrupts of the current priority
level.
Semiconductor Group
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