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Calla – Zilog Z16F2810 User Manual

Page 97

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UM018809-0611

CALLA Instruction

ZNEO

®

CPU Core

User Manual

81

CALLA

Definition

CALL Absolute

Syntax

CALLA dst

Operation

SP

 SP

4

(SP)

 PC

PC

 dst

Description

The CALLA instruction decrements the Stack Pointer (R15) by four and stores the current Pro-
gram Counter value onto the top of the stack. The pushed PC value points to the first instruction
following the CALLA instruction. Then the 32-bit immediate operand is loaded into the Program
Counter and execution of the procedure begins. After the procedure completes, it uses a RET
instruction to pop the previous PC value and return from the procedure.

If the immediate operand is odd, the least significant bit is discarded so that the call destination
address is always an even number.

The CALLA instruction is used to explicitly invoke the 32-bit immediate call opcode in situa-
tions when a fixed opcode size is desired, such as a jump table.

Flags

Flags are not affected by this instruction.

Syntax and Opcodes

Example

Before:

PC=0000_044EH, SP=FFFF_DB22H

CALLA 00352920H

;Object Code: F231 0035 2920

After:

PC=0035_2920, SP=FFFF_DB1EH, FFFF_DB1EH=0000_0454H

Instruction, Operands

Word 0

Word 1

Word 2

CALLA imm32

F231H

imm[31:16]

imm[15:0]

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