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Accessing hi byte of int16 in assembly

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embedded_tom

Joined: 09 Oct 2008
Posts: 4
Location: Long Island, NY

Accessing hi byte of int16 in assembly

Posted: Mon Oct 20, 2008 8:36 am

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I read through the forum and found a way to do this by using the '&' prefix: http://www.ccsinfo.com/forum/viewtopic.php?t=7220

Code:

bcf TMR1ON
movf Next_Time, W
addwf TMR1, F
btfsc C
incf TMR1H, F
movf &Next_Time+1, W

Next_Time is located at 0x28 according to the .lst file:

Code:

Next_Time 00000028

But it doesn't access 0x29 in the second movf!?!

Code:

00484 .................... bcf TMR1ON
0015 1010 00485 BCF 10.0
00486 .................... movf Next_Time, W
0016 0828 00487 MOVF 28,W
00488 .................... addwf TMR1, F
0017 078E 00489 ADDWF 0E,F
00490 .................... btfsc C
0018 1803 00491 BTFSC 03.0
00492 .................... incf TMR1H, F
0019 0A8F 00493 INCF 0F,F
00494 .................... movf &Next_Time+1, W
001A 082A 00495 MOVF 2A,W

Adding parenthesis or dropping the "+1" doesn't work. Next_Time is declared as an int16.

My compiler is Ver 4.080. uP is rfPIC12F675 (12F675 w/RF transmitter).

Ideas?

Thanks.

Tom

RLScott

Joined: 10 Jul 2007
Posts: 465

Re: Accessing hi byte of int16 in assembly

Posted: Mon Oct 20, 2008 8:59 am

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Try this:

Code:

#byte Next_Time_H=Next_Time+1
. . .
movf Next_Time_H,W

This has the advantage of also working outside of the assembly language block as in:

Code:

int k;
k = Next_Time_H;

_________________
Robert Scott
Real-Time Specialties
Embedded Systems Consulting

embedded_tom

Joined: 09 Oct 2008
Posts: 4
Location: Long Island, NY

Re: Accessing hi byte of int16 in assembly
Posted: Tue Oct 21, 2008 7:26 am

Thanks, but got this error for the #byte statement: Error 43 Expecting a declaration. tom

RLScott

Joined: 10 Jul 2007
Posts: 465

Re: Accessing hi byte of int16 in assembly

Posted: Tue Oct 21, 2008 7:30 am

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embedded_tom wrote:

Thanks, but got this error for the #byte statement: Error 43 Expecting a declaration.

tom

Please post the code showing how you used the #byte directive. It is a valid CCS directive. Look it up in the CCS help file.
_________________
Robert Scott
Real-Time Specialties
Embedded Systems Consulting

embedded_tom

Joined: 09 Oct 2008
Posts: 4
Location: Long Island, NY

Posted: Tue Oct 21, 2008 7:34 am

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I did review #byte in the CCS manual. Here's what I used:

Code:

#byte Next_TimeH = Next_Time + 1;

Is #byte similar to "assign" in other compilers?

I just tried this & it worked:

Code:

movf make8(Next_Time,1), W

Thanks for the push in the right direction!

tom

RLScott

Joined: 10 Jul 2007
Posts: 465

Posted: Tue Oct 21, 2008 9:20 am

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embedded_tom wrote:

I did review #byte in the CCS manual. Here's what I used:

Code:

#byte Next_TimeH = Next_Time + 1;

The problem is the ';' at the end. Take it off and it should work.
_________________
Robert Scott
Real-Time Specialties
Embedded Systems Consulting

embedded_tom

Joined: 09 Oct 2008
Posts: 4
Location: Long Island, NY


Posted: Tue Oct 21, 2008 2:30 pm

Yep, that did it. Thanks. tom

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