Using "Change on Port B" int for a serial input in

starfire151 · Joined: 01 Apr 2007 Posts: 195

I'm trying to set up a PIC18LF2525 port bit B4 for recv and bit B5 for xmit for a serial port interface. I set it up on the upper nibble of port B to use the interrupt-on-change feature. I have another serial interface using the hardware port of bits C6 and C7 so I can't use that port for this serial stream. The stream name for the serial input on pins B5 and B4 is "TERM". What I have done so far (with limited success) is something like the following:

treitmey · Joined: 23 Jan 2004 Posts: 1094 Location: Appleton,WI USA

Don't disable the interupt in the interupt service routine.

Just by being in the ISR the compiler turns them off for you,... ie normally you can't be interupted while in the ISR.

(you can also remove the enable)((since you never disable it))

also in other spec sheets I remember seeing that the port B IRQ is cleared when the port is read. try putting

int8 x;
x = input_b();

inside the ISR.

I think others have done this before. Try searching for working code

Ttelmah · Guest

In the 'main, before enabling the interrupt, read portB, and clear the interrupt. Remember that serial data idles 'high', so a change will almost certainly have already been 'seen' on the pin, soon after power-up.
The interrupt will trigger if _any_ of the upper pins change from the latched state. If you use one for output (as you do...), then the interrupt will trigger as soon as you start sending data, which will really stop things working...
Getch, will access the default stream (last one defined), not the 'term' stream, and you will effectively try to read a character from this, then one from 'term'. You need to use 'kbhit(TERM)', not 'getch', in your if statement.
The disable interrupts, will stop subsequent characters until after the print. May well result in data loss.
This is going to be very hard to make work. You would be better re-mapping something from port B0, B1, or B2, and using one oif these interrupts to handle this. Code for this has been published here in the past.

Best Wishes

starfire151 · Joined: 01 Apr 2007 Posts: 195

Thanks for the recommendations. I will try these when I can access to my hardware tonight.

I've tried searching the forum for previous (working) examples of someone trying to do this but my search has probably not been formatted quite correctly (over 4600 hits). Does someone have the link to the previously posted working code example of doing this operation?

Thanks.

Dave

starfire151 · Joined: 01 Apr 2007 Posts: 195

I tried the suggesstions and they worked perfectly!

I did a read on port B before enabling interrupts in the background first. According to the data sheet, the port change interrupt only occurs on pins B4 through B7 set as inputs. I defined only B4 as the serial input. I did a read on port B as the first step in the INT_PB routine. I checked for a complete character by using if(kbhit(TERM)){ } and assigned the character and set a flag. The background routine checked for the flag and, when seen, printed the character.

It worked interactively with the hardware serial port also active.

Thanks for your suggestions!
Very Happy