gnupic: about data tables and shared variables
Subject:
about data tables and shared variables
From:
Lope Vega ####@####.####
Date:
30 Aug 2008 17:17:48 -0000
Message-Id: <192895.18267.qm@web28214.mail.ukl.yahoo.com>
Hello again guys,
First of all, do you recall in my last message when I said all the problems dissapeared for me as soon as I grounded RB3? My mistake, I was tryin to refer to RB5, which I've even read within the specs, should be grounded whether it's not being used.
Said and solved that, I'm running into two problems I cannot cope with, and for which I'd be glad to hear anything about.
One of them is about data tables. I'm trying to drive 3 7-segment displays which I've got multiplexed. Since I don't really yet understand table reads/writes, and haven't seen an example which adequates to what I'm doing, I thought on using `computed gotos':
; make sure they're placed at the begining of a page
my_table_code code 0x200
my_table:
addwf pcl, f
retlw b'01000000' ; number 0
...... ; number 1
display:
; call my table, which will use the value on the `w' register
call my_table
; actually display the number
movwf latb
; and return
retlw 0x0
The problem I'm having is that the PC gets lost.
Though I've been reading within the piclist's archives about how to solve it (working arround with PCLATH), I haven't been able to, so if anyone knows of some example code about this, or about using table reads I can apply to this, or even could write some example code I could start off with, that would be great.
The other problem I'm finding is about shared variables, which would make my life much easier. I have changed the line:
DATABANK NAME=usb4 START=0x400 END=0x4FF PROTECTED
within the default linker script for the pic18f4550, with:
SHAREBANK NAME=usb4 START=0x400 END=0x4FF
I've read the specs says it is risky at best to do this (because of dynamic buffers' allocation policy it claims) but I won't be using USB by now, and any of the ways, as far as I can tell the problem I'm having hasn't got nothing to do with it, as I've tried with other script's lines.
My problem is that if I define a udata_shr block let's say in my main file:
myvars udata_shr
my_global_var res 1
Then, whenever I try to use it on other module I get an "`my_global_var symbol is undefined" message, and I haven't seen some sort of "global" or "extern" directive I should use so as to let my other module know that was a variable declared as shared within the main one.
Any comments appreciated,
Many Thanks.
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