I am writing some routines in assembly for an 18F458 that I want to operate
correctly regardless of what bank they were called from.  I'm trying to save
as many instructions as possible, so this is preferred over context saving for
these particular routines.

To accomplish this goal, I am attempting to use the access bank.  My plan is
to place all variables that these routines use in the access bank and then
specify the access bank on all relevant instructions in these routines.

The problem I am experiencing is that my code works fine when I DON'T specify
the access bank, and doesn't work when I DO specify the access bank.

It is okay to specify the access bank even if the BSR is 0, correct?  Because
that is the situation that my code is failing under.  I haven't tried calling
the routine with the BSR set to anything other than 0 yet.

Has anybody experienced this problem before??

The offending code is at the bottom of this email.  As shown, the code works
great.  The routine is called MAX3110_WRITEHEX and simply writes an 8-bit
number out over serial in ASCII format (i.e. sends the characters 'a' and '1'
instead of the binary value 0xa1).  If I add ", A" to the end of the
instructions that access HEX_NUM and HEX_HIGH, the MAX3110_WRITEHEX routine
does not work.


Thanks,
Eric Christensen



#define HEX_NUM         0x014
#define HEX_HIGH        0x015



MAX3110_WRITEHEX
        dw 0xffff        ; work-around for silicon rev B4 errata #5

        movff HEX_NUM, HEX_HIGH
        ; use swap & and to save two instr maybe
        rrncf HEX_HIGH   ; shift upper nibble of HEX_NUM to
        rrncf HEX_HIGH   ; the lower nibble of HEX_HIGH
        rrncf HEX_HIGH
        rrncf HEX_HIGH

        movlw 0x0f       ; clear the upper nibble of HEX_NUM
        andwf HEX_NUM

        movlw 0x0f       ; clear the upper nibble of HEX_NUM
        andwf HEX_HIGH   ; (shound't need this, but... just in case for now)

        movlw 0x09       ; if the upper nibble is greater than 9, output a-f
(for hex)
        cpfsgt HEX_HIGH
                goto byte_one_low     ; else we can just output the number

                movlw asc_0 + 0x07
                addwf HEX_HIGH
                MAX3110_PUTCHARf HEX_HIGH
                goto byte_two

byte_one_low
        dw 0xffff        ; work-around for silicon rev B4 errata #5
        movlw asc_0
        addwf HEX_HIGH
        MAX3110_PUTCHARf HEX_HIGH

byte_two
        dw 0xffff        ; work-around for silicon rev B4 errata #5
        movlw 0x09       ; if the upper nibble is greater than 9, output a-f
        cpfsgt HEX_NUM
                goto byte_two_low    ; else we can just output the number

                movlw asc_0 + 0x07
                addwf HEX_NUM
                MAX3110_PUTCHARf HEX_NUM
                goto byte_two_done

byte_two_low
        dw 0xffff        ; work-around for silicon rev B4 errata #5
        movlw asc_0
        addwf HEX_NUM
        MAX3110_PUTCHARf HEX_NUM

byte_two_done
        dw 0xffff        ; work-around for silicon rev B4 errata #5

        return
        dw 0xffff        ; work-around for silicon rev B4 errata #5



MAX3110_PUTCHARf macro fADDRESS

        SPI_CONFIG 0x40, 0x00     ; configure the spi module for the MAX3110

        bcf MAX3110_CS, A         ; select the MAX3110
        SPI_SEND_16 0x00, 0x00    ; get the MAX3110 status register
        bsf MAX3110_CS, A         ; de-select the MAX3110
        btfss SPI_RXDATA1, 6, A   ; see if the transfit buffer is full
                goto $-30         ; jump back 15 instructions if it is

        bcf MAX3110_CS, A         ; select the MAX3110
        SPI_SEND_16if 0x80, fADDRESS    ; send out BYTE
        bsf MAX3110_CS, A         ; de-select the MAX3110

        endm

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