Replacing existing pic

[Freman]

G'day there.

I'm sure what I have is a very simple problem, but I'm having a bit of trouble working out the back side to it.

Back story - I'm upgrading my home theater (if it can be called that) to be operated from a single remote through my media PC. I've already gotten most of the other stuff working (with help from here with the comparator stuff I was having problems with before)

I've pulled apart the receiver/controller for my motorized projection screen. Imagin my delight to see it's driven by a PIC chip - unfortunatly the chip that's existing has code protect so I can't just reverse engineer the chip and add my new feature (a 1 wire serial port). I'm forced to try and replicate the code.

I've got a fair understanding of most of it, but the input buttons have me lost.

Attached is a very very basic overview of the circuit that my new pic has to slot into.

How on earth can I tell what button is pushed?

Things I know.

Pin 6 to Pin 7 is 4.7v (it varies a little), pin 6 to gnd is 0.2v (it also varies a little) Pin 7 to gnd is 5v

Can you think of any way they might have been reading the 3 buttons in the original circuit?

Ideally I'd love keep the original RF remote working as well, but as I have no idea what signals it's using (And don't have a scope) I don't know how I can do that

[falingtrea]

If a pin varies a little, it may be changing state faster than the device you are trying to measure it with. I would think the code is doing something with the weak pull-ups on the pins. Fiddling with the weak pull-ups would allow the chip to scan the buttons, and the code may even use the ADC to read pin levels.

[mister_e]

Sure enough they use internal pull-ups. Make sure you disable the ADCs and comparators before.

Now how to know which push button.. Are you sure of the current schematic? Any way it miss some resistors and/or diode in that?

[Freman]

I'm positive there's no missed resistors or diodes in relation to the push buttons - as much as it's a very abbreviated schematic, the circuit really doesn't have much more - I can upload some scans of the board if you like, but I've actually decided to approach this a different way.

Originally I was going to sacrafice the remote control function to gain a serial interface, but what I've since decided to do is take the two outputs from the original pic and feed it into another pic - this will give me my serial interface and keep the remote control - without having to deal

Now I have a problem with frightfully slow interrupts - I've tested this in PIC Simulator and it works reasonably quickly there. In real life tho, this code interrupts 'eventually' usually 5-20 seconds later. I can't see why, I'm only tying it up for 10 ms then I've inserted an extra pauseus so it's got something to interrupt before/after before returning to serin.

Anyway I can speed up the interrupt to... between 11 and 100 ms?

' Configure the pic
@     device pic12F675, INTRC_OSC_NOCLKOUT, WDT_ON, PWRT_ON, MCLR_OFF, BOD_ON, CPD_OFF, PROTECT_OFF

N9600   CON     6

CMCON        = 7
ANSEL        = 0

Relay1       VAR GPIO.5
Relay2       VAR GPIO.4

SlavePower   VAR GPIO.2
SlaveRelay1  VAR GPIO.0
SlaveRelay2  VAR GPIO.1

Serial       VAR GPIO.3

B0           var BYTE

INPUT SlaveRelay1
INPUT SlaveRelay2
INPUT Serial

OUTPUT Relay1
OUTPUT Relay2
OUTPUT SlavePower

ON INTERRUPT GOTO slaveSpeaks
IOC            = %00000011
INTCON       = %10001000

' Turn on the original PIC
HIGH SlavePower

main:
    B0 = 0
    PAUSEUS 1

    SERIN Serial, N9600, 10, main, [1], B0

    ' The original PIC latches it's output, we want to reboot the original pic if we get something from the serial port to force it's outputs low
    IF B0 > 1 THEN LOW SlavePower
    if B0 = 2 THEN GOSUB subUp
    IF B0 = 3 THEN GOSUB subDown
    IF B0 = 4 THEN GOSUB subStop
    IF B0 > 1 THEN
        PAUSEUS 1000
        HIGH SlavePower
    ENDIF
GOTO main

DISABLE
subUp:
    LOW Relay2
    HIGH Relay1
    RETURN
subDown:
    LOW RELAY1
    HIGH Relay2
    RETURN
subStop:
    LOW Relay1
    LOW Relay2
    RETURN

slaveSpeaks:
    if SlaveRelay1 THEN
        GOSUB subUp
    ELSE
        IF SlaveRelay2 THEN
            GOSUB subDown
        ELSE
            GOSUB subStop
        ENDIF
    ENDIF
    INTCON = %10001000
    RESUME
ENABLE

[mister_e]

I would probably skip the interrupt and perform everything in a tight loop instead. As the Relay check is done pretty quick. Not a fan of using GOSUBs in a ISR.

From what i feel, S2 should have dual contacts attach to GPIO<1:0>

To know which relay is activated, i would bet that...

WhichRelay VAR BYTE
'
'
'
'
WhichRelay=GPIO & 3
Select case WhichRelay
    CASE 0 ' Relay 2
      ' do stuff for relay 2

    CASE 1 ' Relay 1
      ' do stuff for relay 1
 
    CASE 2 ' Relay 3
      ' do stuff for relay 3
     END SELECT

If you still want to use Ints, don't re-enable the GIE bit, the PIC will do it for you. Just clear the offending INT flag and get out of there.

If you play with GIE bit, you will run into problems, that's for sure.

[Freman]

Heh, never even thought about SELECT CASE

So something more like this then.

' Configure the pic
@     device pic12F675, INTRC_OSC_NOCLKOUT, WDT_ON, PWRT_ON, MCLR_OFF, BOD_ON, CPD_OFF, PROTECT_OFF

N9600   con     6

CMCON        = 7
ANSEL        = 0

Relay1       VAR GPIO.5
Relay2       VAR GPIO.4

SlavePower   VAR GPIO.2
SlaveRelay1  VAR GPIO.0
SlaveRelay2  VAR GPIO.1

Serial       VAR GPIO.3

B0           var BYTE
SlaveState   VAR BYTE
WhichRelay   VAR BYTE

INPUT SlaveRelay1
INPUT SlaveRelay2
INPUT Serial

OUTPUT Relay1
OUTPUT Relay2
OUTPUT SlavePower

restart:
SlaveState = 0
PAUSEUS 1000
HIGH SlavePower

main:
    B0 = 0
    pauseus 1
    SERIN Serial, N9600, 10, main, [1], B0
    IF B0 > 1 THEN LOW SlavePower
    if B0 == 2 THEN GOSUB subUp
    IF B0 == 3 THEN GOSUB subDown
    IF B0 == 4 THEN GOSUB subStop
    IF B0 > 1 THEN GOTO restart
    
    WhichRelay = GPIO & 3
    IF SlaveState <> WhichRelay THEN
        SlaveState = WhichRelay
        SELECT CASE WhichRelay
            CASE 0
                GOSUB subStop
            CASE 1
                GOSUB SubUp
            Case 2
                GOSUB subDown
        END SELECT
    ENDIF   
goto main

subUp:
    LOW Relay2
    HIGH Relay1
    RETURN 
subDown:
    LOW RELAY1
    HIGH Relay2
    RETURN
subStop:
    LOW Relay1
    LOW Relay2
    RETURN