User guide

DS4830A User’s Guide
206
{L/S}CALL src {Long/Short} Call to Subroutine
Description: Performs a call to the subroutine destination specified by src. The CALL instruction uses an
8-bit immediate src to perform a relative short call (IP +127/-128 words). The CALL
instruction uses a 16-bit immediate src to perform an absolute long CALL to the specified
16-bit address. The PFX[0] register is used to supply the high byte of a 16-bit immediate
address for the absolute long CALL. Using the optional ‘L’ prefix (i.e. LCALL) will result in
an absolute long call and use of the PFX[0] register. Using the optional ‘S’ prefix (i.e.
SCALL) will attempt to generate a relative short call, but will be flagged by the assembler if
the destination is out or range. Specifying an internal register src (no matter whether 8-bit or
16-bit) always produces an absolute CALL to a 16-bit address, thus the ‘L’ and ‘S’ prefixes
should not be used. The PFX[n] register value is used to supply the high address byte when
an 8-bit register src is specified.
Status Flags: None
Operation: @++SP  IP + 1 PUSH
IP  src Absolute CALL
IP  IP + src Relative CALL
Encoding: 15 0
f011
1101
ssss
ssss
Example(s): CALL label1 ; relative call to label1 (must be within IP +127/ -
; 128 address range)
CALL label1 ; absolute call to label1 = 0120h
; MOVE PFX[0], #01h
; CALL #20h.
CALL DP[0] ; DP[0] holds 16-bit address of subroutine
CALL M0[0] ; assume M0[0] is an 8-bit register
; absolute call to addr16
; high(addr16)=00h (PFX[0])
; low (addr16)=M0[0]
MOVE PFX[0], #22h ;
CALL M0[0] ; assume M0[0] is an 8-bit register
; high(addr16)=22h (PFX[0])
; low (addr16)=M0[0]
LCALL label1 ; label=0120h and is relative to this instruction
; absolute call is forced by use of ‘L’ prefix
; MOVE PFX[0], #01h
; CALL #20h
SCALL label1 ; relative offset for label1 calculated and used
; if label1 is not relative, assembler will generate an error
SCALL #10h ; relative offset of #10h is used directly by the CALL