getting confusing

[2camjohn]

I had my 16f82a (edit 16f628 thanks Exo) set up with an external comparator.

Now I want to use the internal comparator to save space, the problem is I had all my inputs using port B and my outputs using port A.

From reading the datasheet the comparator can only be used on pins RA0 - 3

I am using interrupts from port b.0

Im really confused as to how to set up my inputs and outputs:

Here is what I want io wise:

18 RA1,AN1 - Output - solenoid driven by transistor
1 Vref,AN2,RA2 Comparator reference voltage (from pot)
2 CMP1,AN3,RA3 Comparator non inverting input (ie when this value is above reference the output is 1)
6 INT,RB0 Interrupt trigger
7 RX,DT,RB1 Output - led
8 TX,CK,RB2 Output - led

Util now I have been able to configure the outputs just by saying all portA is an output (TRISA = 0x00) but now it has suddenly got alot more complicated.
Can someone explain how to set this up, or better yet give me the code to do it as I am pretty confused.

Also how do I access the output of the comparator (i know this is in the datasheet but they are quite hard to comprehend in places)

Thanks in advance for your time,
John

 

[2camjohn]

Anyone, as the title says im really confused :? :cry:

 

[Exo]

Pic16F82A? that doesn't exist. Need the correct type first.

 

[2camjohn]

Thanks for your time Exo,

Im sorry about the typing mistake (when you have been pouring over the data sheets as long as I have, letters and numbers all seem to bleed into one big blur :? )

The chip in question is the 16f628

Your's 'sitting here pressing F5'
John

 

[2camjohn]

Exo are you typing up a long and helpful reply or were you just getting my hopes up?

 

[Exo]

First of all, since you need only one comparator, its best to connect comparator inputs to RA1 and RA2. A comparator mode between RA3 and RA2 isn't available as you can see in the datasheet page 56.
So The new settings are:
RA1: Comparator reference (from pot)
RA2: Comparator input (when this value is above ref output is 1)
RA3: Output - solenoid driven by transistor
Port B stays the same. You can use another portA pin to drive the solenoid, but the comparator should stay on RA1-RA2

MOVLW   b'  00000101'
MOVWF   CMCON              ;load comparator settings 
BSF     STATUS, RP0        ;Switch to bank 1
BSF     TRISA, 1
BSF     TRISA, 2           ;RA1 - 2 input for comparator
BCF     TRISA, 3           ;RA3 output for solenoid
BSF     TRISB, 0           ;RB0 input for interrupt trigger
BCF     TRISB, 1       
BCF     TRISB, 2           ;Led outputs
BSF     STATUS, RP0        ;Switch back to bank 0

The comparator output can be read from CMCON - bit 7

 

[2camjohn]

Thanks alot Exo,

I am now happy that I am on the right track.
Everything is much clearer now.

 

[2camjohn]

Hi

I used the settings you said but they dont appear to work.

On my simulator it works fine but when I program my chip nothing happens, when tested in my programme the value of cmcon bit 7 is always at 0.

 

[2camjohn]

I think it is working actually, im just a fool.

Thanks