Soon Kyu Lee's Blog – February 2013 Archive (2)

Few things that took me a while to figure out:

1. When using high and low priority interrupts, GIEH must ALSO be enabled along with GIEL (bits 7 and 6) for low priority interrupts to occur.

2. Even when interrupts are not enabled (such as external interrupts on INT0), these are still being flagged. Thus, if there are multiple sources of interrupts and if the interrupt source checking is not handled carefully, disabled interrupt routines may still occur. For example, in my…

Code given in textbook is something like this:

WR_INS

bcf RS ;clear Register Status bit

movwf temp_lcd ;store instruction

andlw 0xF0 ;mask 4 MSB

movwf LATD ;send 4 MSB

bsf E ;pulse enable high

call delay5ms

swapf temp_lcd, 0 ;swap nibbles (result into WREG)

andlw 0xF0 ;mask 4 LSB

bcf E

movwf LATD ;send 4 LSB

bsf E ;pulse enable high

nop

bcf E

call delay5ms ;allow time for change

return

But this does not…