Hi David,
I know using res is more comfortable, and I would like to do that, but it=
 doesn't work for me.
I create a new project for testing it again, (MPASM project, not MPLINK) =
for PIC17C756A with only one file, and the following code:

;; BEGIN CODE

        LIST            p=3D17C756a
        #include <p17c756a.inc>       ; processor specific variable definitions

        __CONFIG        _WDT_OFF & _XT_OSC & _BODEN_ON & _MC_MODE

              org 0x0000
              goto START

                org 0x8
                goto START

                org 0x10
                goto START
        =09
                org 0x18
                goto START

                org 0x20
                goto START

        org 0x21

var1    res 1
var2    res 1
test1   res 1
test2   res 1

START
        goto START

        end

;; END CODE

Then I compile, and I click on Window->Modify. In the list of variables, =
I type var1, or test1 or whatever variables you want (from the four I res=
erved), and I can't find=20
them.
Maybe you noticed I was not using UDATA. If I place it just before "var1 =
res 1", I get a compiler error:
Error[149]   E:\PRUEBA\MPLAB\PRUEBA\RES_EQU\RES_EQU.ASM 23 : Directive on=
ly allowed when generating an object file

 Also, if you look at the device datasheet (DS30264A), page 37, there is =
an example of an interrupt service routine. I copy it here:

; The addresses that are used to store the CPUSTA and WREG values must be=
 in the data memory
; address range of 1Ah - 1Fh. Up to 6 locations can be saved and restored=
 using the MOVFP
; instruction. This instruction neither affects the status bits, nor corr=
upts the WREG register.
;
UNBANK1         EQU 0x01A ; Address for 1st location to save
UNBANK2         EQU 0x01B ; Address for 2nd location to save
UNBANK3         EQU 0x01C ; Address for 3rd location to save
UNBANK4         EQU 0x01D ; Address for 4th location to save
UNBANK5         EQU 0x01E ; Address for 5th location to save
                           ; (Label Not used in program)
UNBANK6         EQU 0x01F ; Address for 6th location to save
                        ; (Label Not used in program)
;
                : ; At Interrupt Vector Address
PUSH=20
        MOVFP ALUSTA, UNBANK1           ; Push ALUSTA value
        MOVFP BSR, UNBANK2              ; Push BSR value
        MOVFP WREG, UNBANK3             ; Push WREG value
        MOVFP PCLATH, UNBANK4           ; Push PCLATH value
;
: ; Interrupt Service Routine (ISR) code
;
POP=20
        MOVFP UNBANK4, PCLATH           ; Restore PCLATH value
        MOVFP UNBANK3, WREG             ; Restore WREG value
        MOVFP UNBANK2, BSR              ; Restore BSR value
        MOVFP UNBANK1, ALUSTA           ; Restore ALUSTA value
;
        RETFIE ; Return from interrupt (enable interrupts)

As you can see, this example uses EQU for the address of the location (UN=
BANK1, for example) to save the registers, before the interrupt service r=
outine code.

I know using "res" is the way to work with some other devices, but with t=
his device, the way seems to be working with "equ"...

Carlos



25/05/01 0:22:47, David Cary <dcary@BRUNSWICKOUTDOOR.COM> escribi=F3:
>
>Dear Carlos Nieves =D3nega,
>
>Carlos Nieves =D3nega <cnieves@TSC.UVIGO.ES> on 2001-05-24 08:56:13 AM m=
entioned
>>Subject: Re: [PIC]: PIC C compiler & MPLAB
>...
>>when I begin programming my chip (pic17c756) (in assembler). I have var=
iables
>coded as:
>>
>>var1    res 1
>
>Every single one of my variable locations are defined using "res", just =
like
>this.
>
>>and they weren't shown in the list.
>
>It works for me. When I open the ``file register window'' and right clic=
k on a
>byte, I get the ``Modify'' dialog box. All of my variables are listed in=
 the
>little drop-down ``address'' field. I modify them all the time when I'm
>single-stepping through the code using MPLAB ICD.
>
>>The problem
>
>What problem ? It works fine for me.
>
>>was I misunderstood the assembler,
>>and this assembler directive reserves a byte in program memory
>>(which is
>>EPROM, so you can't modify it while executing code).
>>The solution was declare the variable as an address:
>>
>>var1    equ 0x05                (Data address 0x05)
>
>I like to distinguish between reserving a byte of RAM for a variable (us=
ing
>``res''), vs. defining a constant (using ``equ''). When I accidentally p=
lace 2
>variables in the same RAM location, ``res'' gives me a nice warning tell=
ing me
>exactly where the problem is, but ``equ'' compiles without warning, leav=
ing me
>mystified when it doesn't do what I expected at runtime.
>
><pre>
>screen_array   UDATA     ; Let linker allocate space for these.
>     ; backup of screen for double-buffering
>screen         res (64*12/8)
>...
>
>test_buffers   UDATA_SHR ; Let linker allocate space for this in unbanke=
d RAM.
>buffer3   res 1
>buffer2 res 1
>
>...
>
>;***** BAUD RATES *****
>;
>B9600          EQU  129       ;9600 BAUD
>B19200         EQU  64        ;19200 BAUD
>B38400         EQU  32        ;38400 BAUD
>...
>
>font_subs CODE
>
>; uses 1 stack
>; given a character in w, copy
>; the pixels of that character
>; from the ``medium_font''
>; to ``screen'' buffer
>copy_character_to_screen_buffer:
>     ; Look up starting address in table
>     addlw (0 - ' ') ; (table starts with space character)
>...
>     return
></pre>
>
>--
>David Cary
>
>

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