ISD51 User's Guide

SFR Access

The 8051 provides no indirect access to SFRs. For this reason, ISD51 must include specific functions to read and write the SFRs of your target. These functions are named ?ISD?READSFRxx and ?ISD?WRITESFRxx (where xx is simply a sequence number starting with 00).

By default, ISD51 includes all the necessary read functions. You should not modify or delete any of these routines from the ISD51.A51 file.

ISD51 includes only a few functions to write to SFRs. These functions are listed in the ISD51.A51 file. If you write to SFRs from within the µVision IDE, corresponding functions must be available in ISD51.A51. By default, only a few functions are provided (ACC, B, DPH, DPL, P0, P3, PSW, and SP).

Use the following example as a template for your own SFR write routines. This template writes to the SFR at address 0xA5.

;--------------------------------------------------------------------------
; Command: Write SFR04:  SFR:0xA5
;  LOW (?ISD?WRITESFR04), HIGH (?ISD?WRITESFR04), dummy, SFR:0xA5
;
PUBLIC ?ISD?WRITESFR04
?ISD?WRITESFR04:
                MOV     0A5H,A
                AJMP    ?ISD?CMDLOOP