What am I doing wrong? 16F628A

Hi Guys,

It should be pretty straight forward, but I'm at a loss. Trying to use a 16F628A and tried searching online for similar issues, but have been unsuccessful in resolving the matter.

I wrote out a large amount of code. Found that one of the outputs on the PIC wasn't doing what it was suppose to do. To make a long story short, I wrote a small bit of code to test the outputs I wanted to control and it's still not working. I tried programming new chips, and get the same result.

My problem: porta.4 (pin 3) does not want to turn on. It stays low and does not activate to control a transistor. I replaced the transistor (in case it was bad), and get the same result. Can someone tell me what I'm missing.

Thanks,
Tony

Code:

---

#CONFIG
  __config _INTRC_OSC_NOCLKOUT & _WDT_ON & _LVP_OFF & _CP_OFF & _PWRTE_ON & _MCLRE_OFF & _BOREN_OFF
#ENDCONFIG

Reset:

  CMCON = 7                    ' Analog comparators off
  VRCON = 0                    ' A/D Voltage reference disabled
  TRISA = %11000001            ' sets pin as input (1) or output (0)
  TRISB = %00110011            ' sets pin as input (1) or output (0)
  PORTA = %00000000            ' sets outputs as high (1) or low (0)
  PORTB = %00000000            ' sets outputs as high (1) or low (0)

' -----[ Variables ]-------------------------------------------------------
 
    rightrelay    var  porta.1  ' right relay output
    leftrelay    var  portb.2  ' left relay output

    rightfet      var  porta.4  ' right fet output
    leftfet      var  porta.2  ' left fet output

high leftrelay
high rightrelay

action:

low leftfet
high rightfet

pause 500

low rightfet
high leftfet

pause 500

goto action

---

PortA.4 is an open drain port. You must use a pullup resistor in order to drive your transistor.

Cheers

Al.

Hi;

To complement aratti answer, that information is on the Datasheet.

I'm using an npn, so using a pull-up resistor turns on my transistor. Any other thoughts, or an equivalent chip to the 628A that does not have an open drain output?

Thanks,
Tony

Use the pullup and reverse your high and low. up is down and down is up...

Or use a PNP, or invert the signal with another transistor or use an 16F88, 16F819, 16F1826 etc etc.
If buying new, go for the enhanced 16F1xxx series, cheaper and better in all respects I can think of.

Selecting 8-bit chips with 18 pins in the Microchip Advanced Part Selector, gives 17 different parts, pick one and look at the datasheet.

/Henrik.

Unfortunately, I'm using an npn to control a p-channel mosfet, so I can't change the layout. Thank you for the link. That is extremely helpful.

Tony