Atmel C51 Handbuch Seite 44

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Seitenansicht 43
The 8051 Instruction Set
Atmel 8051 Microcontrollers Hardware Manual 1-42
4316E–8051–01/07
1.14.25 JZ rel
1.14.26 LCALLaddr16
Function: Jump if Accumulator Zero
Description: If all bits of the Accumulator are 0, JZ branches to the address indicated; otherwise, it proceeds with the next
instruction. The branch destination is computed by adding the signed relative-displacement in the second
instruction byte to the PC, after incrementing the PC twice. The Accumulator is not modified. No flags are
affected.
Example: The Accumulator originally contains 01H. The following instruction sequence,
JZ LABEL1
DEC A
JZ LABEL2
changes the Accumulator to 00H and causes program execution to continue at the instruction identified by the
label LABEL2.
Bytes: 2
Cycles: 2
Encoding: 0 1 1 0 0 0 0 0 rel. address
Operation: JZ
(PC) (PC) + 2
IF (A) = 0
THEN (PC) (PC) + rel
Function: Long call
Description: LCALL calls a subroutine located at the indicated address. The instruction adds three to the program counter to
generate the address of the next instruction and then pushes the 16-bit result onto the stack (low byte first),
incrementing the Stack Pointer by two. The high-order and low-order bytes of the PC are then loaded,
respectively, with the second and third bytes of the LCALL instruction. Program execution continues with the
instruction at this address. The subroutine may therefore begin anywhere in the full 64K byte program memory
address space. No flags are affected.
Example: Initially the Stack Pointer equals 07H. The label SUBRTN is assigned to program memory location 1234H. After
executing the instruction,
LCALL SUBRTN
at location 0123H, the Stack Pointer will contain 09H, internal RAM locations 08H and 09H will contain 26H and
01H, and the PC will contain 1234H.
Bytes: 3
Cycles: 2
Encoding: 0 0 0 1 0 0 1 0 addr15-addr8 addr7-addr0
Operation: LCALL
(PC) (PC) + 3
(SP) (SP) + 1
((SP)) (PC
7-0
)
(SP) (SP) + 1
((SP)) (PC
15-8
)
(PC) addr
15-0
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