Post by thread:16C74 Interrupt Routine

Greetings I am using a 16C74 with TMR0 providing interrupts at a fixed rate. I have to save values during the interrupt routine so I made use of the example given in the data manual to save Status and W registers in RAM. This is the part that is causing problems. >From the data manual: "Example 14-1 and Example 14-2 store and restore the STATUS and W registers. For the PIC16C74 and PIC16c73, the register, W_TEMP, must be defined in both banks and must be defined at the same offset from the the bank base address (i.e., if W_TEMP is defined at 0x20 in bank0, it must also be defined at 0xA0 in bank 1)." My problem is that defining W_TEMP in both banks produces an error. I have made use of the CBLOCK directive to define W_TEMP. Should I be making use of some other way of defining W_TEMP? TIA Victor Moisey Institute of Child Health Red Cross Childrens Hospital Private Bag Rondebosch 7700 Cape Town South Africa

> From: Victor Moisey [spam_OUTVMOISEYTakeThisOuTICH.UCT.AC.ZA] > From the data manual: > "Example 14-1 and Example 14-2 store and restore the STATUS and W > registers. For the PIC16C74 and PIC16c73, the register, > W_TEMP, must be > defined in both banks and must be defined at the same offset > from the the > bank base address (i.e., if W_TEMP is defined at 0x20 in > bank0, it must > also be defined at 0xA0 in bank 1)." > My problem is that defining W_TEMP in both banks produces an > error. Put the lines W_TEMP equ 20 W_TEMPBk1 equ W_TEMP+80 into your code, that's all. The command "movwf W_TEMP" in the interrupt will now addresses 20 or a0, depending on STATUS,RP0. The definition of W_TEMPBk1 is just for your remembrance, that a0 is in use. Martin Gramatke

On Mon, 2 Nov 1998 14:24:35 SAST-2 Victor Moisey <.....VMOISEYKILLspam@spam@ICH.UCT.AC.ZA> writes: >My problem is that defining W_TEMP in both banks produces an error. I >have >made use of the CBLOCK directive to define W_TEMP. Something like this should work: cblock h'20' W_TEMP ;Stores W during interrupt .... (other variables) endc cblock h'a0' W_TEMP1 ;Must be same place as W_TEMP, but in bank 1. .... (Other variables) In the program, always use W_TEMP. W_TEMP1 is defined just to save a place for it. A further refinement would be to have the assembler check that W_TEMP1 is indeed offset from W_TEMP by exactly 80h and issue an error if not: IF (W_TEMP1 != W_TEMP + h'80') error "Bad assignment of W_TEMP1" ENDIF It's been a while since I used an IF directive so this example may not be correct. ___________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com/getjuno.html or call Juno at (800) 654-JUNO [654-5866]