Subject:
Re: [gnupic] about data tables and shared variables
From:
Jerry Zdenek ####@####.####
Date:
30 Aug 2008 18:00:07 -0000
Message-Id: <48B989A3.2030009@sarpeidon.net>
The CALL instruction doesn't update PCLATH. So when you add W to PCL,
PC[15:8] gets whatever is left in PCLATH, causing you to jump apparently
randomly. Set PCLATH first and you should be fine. You should also
make sure PCLATU is cleared just in case it got changed, as that gets
fed into PC as well.
This should work (but I haven't tried it):
my_table_code code 0x200
my_table:
movwf temp_var
clrf PCLATU
movlw HIGH my_table
movwf PCLATH
movf tmp_var,W
addwf pcl, f
retlw b'01000000' ; number 0
....
As for your second problem, at least in MPASM, you need to declare your
variable global as such:
GLOBAL my_global_var
And then when you use it:
extern my_global_var
Jerry
Noel Henson wrote:
> I've had some trouble in the past with this. Don't know if this will help
> but try placing a NOP after the addwf PCL,f. The other thing you will want
> to check is to make sure that your table does not cross a 256-byte
> boundary. If it does, you could actually be branching to to before the
> beginning of the table when you access table values that are above the next
> 256-byte boundary.
>
> I hope this helps,
>
> Noel
>
> On Saturday 30 August 2008, Lope Vega wrote:
>> 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.
>>
>>
>>
>> __________________________________________________
>> Correo Yahoo!
>> Espacio para todos tus mensajes, antivirus y antispam ¡gratis!
>> Regístrate ya - http://correo.yahoo.es
>>
>>
>> ---------------------------------------------------------------------
>> To unsubscribe, e-mail: ####@####.####
>> For additional commands, e-mail: ####@####.####
>
>
>
