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CALL
Subroutine
Syntax
CALL
Operation
dst
SP − 2
PC
tmp
Description
A subroutine call is made to an address anywhere in the 64K address space.
All addressing modes can be used. The return address (the address of the
following instruction) is stored on the stack. The call instruction is a word
instruction.
Status Bits
Status bits are not affected.
Example
Examples for all addressing modes are given.
CALL
CALL
CALL
CALL
CALL
CALL
CALL
dst
−> tmp
dst is evaluated and stored
−> SP
−> @SP
PC updated to TOS
−> PC
dst saved to PC
#EXEC
; Call on label EXEC or immediate address (e.g. #0A4h)
; SP−2 → SP, PC+2 → @SP, @PC+ → PC
EXEC
; Call on the address contained in EXEC
; SP−2 → SP, PC+2 → @SP, X(PC) → PC
; Indirect address
&EXEC
; Call on the address contained in absolute address
; EXEC
; SP−2 → SP, PC+2 → @SP, X(0) → PC
; Indirect address
R5
; Call on the address contained in R5
; SP−2 → SP, PC+2 → @SP, R5 → PC
; Indirect R5
@R5
; Call on the address contained in the word
; pointed to by R5
; SP−2 → SP, PC+2 → @SP, @R5 → PC
; Indirect, indirect R5
@R5+
; Call on the address contained in the word
; pointed to by R5 and increment pointer in R5.
; The next time—S/W flow uses R5 pointer—
; it can alter the program execution due to
; access to next address in a table pointed to by R5
; SP−2 → SP, PC+2 → @SP, @R5 → PC
; Indirect, indirect R5 with autoincrement
X(R5)
; Call on the address contained in the address pointed
; to by R5 + X (e.g. table with address starting at X)
; X can be an address or a label
; SP−2 → SP, PC+2 → @SP, X(R5) → PC
; Indirect, indirect R5 + X
Instruction Set
RISC 16−Bit CPU
3-29
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