Post by thread:PCLATH isn't working

My simulator is showing different response than that of microchip data book. Since the system is also crashing simulator isn't wrong. The problem is: PCLATH doesn't show the wright value after RETFIE. After Timer2 interrupt Top Of Stack (TOS) is 0x8D2, in bank1, after ISR RETFIE instruction is executed. Program goes to 0x8D3 but PCLATH stays zero unchanged, however PCL is changed to 0xD3. I expect PCLATH to show 0x08 but does not. Then why am I at the 0x8D3 address in the program memory? I have no access to stack manually solve this problem. Any help is apreciated. Thank you. Aydin Yesildirek VGT, Panama

On Tue, Jun 10, 1997 at 11:39:54AM +0000, Aydin Yesildirek wrote: > The problem is: PCLATH doesn't show the wright value after RETFIE. The RETFIE instruction (or any other return instruction) does NOT update PCLATH. The stack is 14 bits wide, and stores the whole PC, of which only 8 bits is visible in PCL. The PCLATH register is NOT the upper 8 bits of the PC, but just a holding register that is copied to the high bits of the PC whenever you explicitly change PCL (by a goto, movf etc.). What you have to do is save PCLATH on entry to your ISR, and restore it on exit. This is necessary if you have any goto's in the ISR, and your PIC has more than one ROM page. You also need to zero PCLATH in the ISR, after saving it, of course, but I suspect you are already doing that. -- Clyde Smith-Stubbs |HI-TECH Software, |Voice: +61 7 3354 2411 spam_OUTclydeTakeThisOuThtsoft.com |P.O. Box 103, Alderley,|Fax: +61 7 3354 2422 http://www.htsoft.com|QLD, 4051, AUSTRALIA. |PGP: finger .....clydeKILLspam@spam@htsoft.com --------------------------------------------------------------------------- Download a FREE beta version of our new ANSI C compiler for the PIC microcontroller! Point your WWW browser at http://www.htsoft.com/

> What you have to do is save PCLATH on entry to your ISR, and restore > it on exit. This is necessary if you have any goto's in the ISR, and > your PIC has more than one ROM page. You also need to zero PCLATH in > the ISR, after saving it, of course, but I suspect you are already > doing that. I tried that, but after the interrupt pclath is showing the new address value. I need to get upper portion of top of stack and update my pclath with that value at the end of the ISR. I thought c-complier was supposed to handle this updating pain but not working in my case. I am trying to avoid it by staying within first 2K of the program memory by now. Regards, Aydin > -- > Clyde Smith-Stubbs |HI-TECH Software, |Voice: +61 7 3354 2411 > clydeKILLspamhtsoft.com |P.O. Box 103, Alderley,|Fax: +61 7 3354 2422 > http://www.htsoft.com|QLD, 4051, AUSTRALIA. |PGP: finger .....clydeKILLspam.....htsoft.com > --------------------------------------------------------------------------- > Download a FREE beta version of our new ANSI C compiler for the PIC > microcontroller! Point your WWW browser at http://www.htsoft.com/ >