On Monday, May 24, 2004, at 20:25 US/Pacific, Rafael Vidal Aroca wrote:

>    It's part of picnic project (http://picnic.sf.net) - in the file
> webpic.asm
>
>    This code receives an ISA_OFFSET to address an register inside an
> ISA board that is connected to the pic.
>    ISA_HBASEIO and ISA_LBASEIO are the 2 bytes that makes the fixed
>>

Yuck.  It looks like the difficulty is because the address bus (if I'm
reading the rather unlabled schematic correctly) is split across the 6
low bits of portC (low bits?) and 4 high bits bits of portb.

>>    i'm having trouble converting this asm code that runs on a pic
>> 16F877 to CCS C. I tried to convert it, but it did not work :(
>>
>>    I'd be really thankful if anyone could translate this code into C
>> so that i can compare with what i did.
>>
>>        movlw   ISA_HBASEIO
>>        movwf   ISA_HADR
>>
>>        movf    ISA_OFFSET, W
>>        addlw   ISA_LBASEIO
>>        movwf   ISA_LADR
>>
this computes the actual address:
        ISA_HADR = ISA_HBASEIO;
        ISA_LADR = ISA_OFFSET + ISA_LBASEIO;
That was obvious enough.

>>        ; parse address
>>
>>        movf    ISA_LADR, W
>>        andlw   0x3F
>>        movwf   PORTC

     PORTC = ISA_LADR & 0x3F;

Now we get into interesting "logic."
>>        rrf     ISA_LADR, F
>>        rrf     ISA_LADR, W
>>        andlw   0x30
>>        movwf   ISA_LADR

This takes the two bits that we didn't send to portC, and puts them in
the 0x30 position in W (and ISA_LADR, which .. isn't, anymore.)
I'd rewrite it (from a pure C point of view)
        ISA_LADR = (ISA_LADR & 0xC0) >> 2;
>>
>>        swapf   ISA_HADR, F
>>        rlf     ISA_HADR, F
>>        rlf     ISA_HADR, W
>>        andlw   0xC0
>>        movwf   ISA_HADR
this puts the two low bits of ISA_HADR in the C0 bit positions of W and
ISA_HADR.  the rest of ISA_HADR goes away...
        ISA_HADR = (ISA_HADR & 0x3) << 6;
>>
>>
>>        movlw   0x0F
>>        addwf   ISA_LADR, W
>>        addwf   ISA_HADR, W
>>        movwf   PORTB

I'm not sure what they're doing with the low bits of portB, but I see:
        PORTB = 0xF +      /* Low bits */
             ISA_LADR + /* 0x30 bits */
                    ISA_HADR;  /* 0xC0 bits */

Is that more or less what you came up with?

BillW

--
http://www.piclist.com hint: To leave the PICList
mailto:piclist-unsubscribe-request@mitvma.mit.edu