16F628A and RA5 (MCLR pin)

Hi, after reading Melanie's excellent tutorial on programming fuses, I started a program that uses every pin of the uC, 14 are used for driving 2x 7 segments display and the other two are used for a couple of buttons.

My problem is with th RA5 pin, I want it to be an output, but I cant make it work that way, its just off, cant use it, so the connected segment is obviously always off, here is the header im using:

@ DEVICE pic16F628a, INTRC_OSC_NOCLKOUT
' System Clock Options
@ DEVICE pic16F628a, WDT_ON
' Watchdog Timer
@ DEVICE pic16F628a, PWRT_ON
' Power-On Timer
@ DEVICE pic16F628A, MCLR_OFF
' Master Clear Options (Internal)
@ DEVICE pic16F628a, BOD_Off
' Brown-Out Detect
@ DEVICE pic16F628a, LVP_OFF
' Low-Voltage Programming
@ DEVICE pic16F628a, CPD_ON
' Data Memory Code Protect
' Set to CPD_OFF for Development Copy
' Set to CPD_ON for Release Copy
@ DEVICE pic16F628a, PROTECT_ON
' Program Code Protection
' Set to PROTECT_OFF for Development Copy
' Set to PROTECT_ON for Release Copy

trisb =%10000000
trisa =%10000000
cmcon =%00000111 'Comparators Off
vrcon =%00000000
intcon =%00000000

as you see buttons are on pin 7 of each port.


What else I need to set to use RA5?


I sill didnt protoboarded it, im just simulating with preteus vsm, and besides the ra5 segment, program works 100 as expected.


Thanks in advance

RA5 (MCLR) cannot be used as an output. You may only use it as MCLR or input.

Jerson

Ok, so if I swap one of the segments with one of the switchs it should work? say for example ra7 swapped for ra5 and set trisa as:

trisa=%00100000

Do I need to change something else?


Thanks

you're right! nothing else to change

I just tried the attached circuit with this code:

@ DEVICE pic16F628a, INTRC_OSC_NOCLKOUT
@ DEVICE pic16F628a, WDT_ON
@ DEVICE pic16F628a, PWRT_ON
@ DEVICE pic16F628A, MCLR_OFF
@ DEVICE pic16F628a, BOD_Off '(off si es muy baja la alimentacion)
@ DEVICE pic16F628a, LVP_OFF
@ DEVICE pic16F628a, CPD_Off
@ DEVICE pic16F628a, PROTECT_Off


trisb =%00000000
trisa =%00100000
cmcon =%00000111 'Comparators Off

porta=0
portb=0
loop:
if porta.5=1 then
porta.4=1
porta.3=0
else
porta.3=1
porta.4=0

endif
goto loop

and it only lits the led on ra3

Any idea? Maybe its a simulator issue (proteus vsm)

Thanks

PORTA.4 is an open drain type. so you can't really drive it like that... you can drive it low but not high... well not directly.

BTW you really need to a resistor in serie with your LEDs to limit the current.

Thanks Steve, I changed common cathode for common anode display and now it works as expected!!