16F628A and RA5 (MCLR pin)

[peu]

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

[Jerson]

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

Jerson

[peu]

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

[mister_e]

you're right! nothing else to change

[peu]

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

[mister_e]

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.

[peu]

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