porta 4 won't come high 16f876

[Neiwiertz]

I'm using a 16f876

pins a0 (input) a1 a2 a3 a5 will work but a4 not
i will to have that a4 is an output so i can drive a led on this pin

i'm using pic basic

DEFINE OSC 4 'CLOCK FREQUENTIE IS 4MHZ'

TRISC = %00000000
TRISA = %00000001
Adcon1 = %00000111
adcon0 = %00000000



TIJD var word

KNOPPEN var byte
XRICHTING var byte
YRICHTING var byte

MAIN:

'GOTO MEETTIJD
'IF (TIJD>2500)OR(TIJD<3500) THEN
'PORTA.5 = 0


'pause 1000

'ELSE
'PORTA.4 = 0
PORTA.1 = 1
PORTA.2 = 1
PORTA.3 = 1
PORTA.4 = 1
PORTA.5 = 1

'pause 1000
'ENDIF

GOTO MAIN


MEETTIJD:
pulsin PORTA.0, 1, TIJD

RETURN

ZENDNAARUSB:

PORTA.1 = 0
PORTA.2 = 0
PORTA.3 = 0
PORTC = 0

KNOPPEN = 32
XRICHTING = 128
YRICHTING = 255


PORTC = KNOPPEN
PORTA.1 = 1
PAUSE 100
PORTC = 0
PAUSE 100
PORTA.1 = 0

pauseus 1

PORTC = XRICHTING
PORTA.3 = 1
pauseus 1
PORTA.3 = 0

pauseus 1

PORTC = YRICHTING
PORTA.2 = 1
pauseus 1
PORTA.2 = 0

pauseus 1

RETURN


END

 

[Nigel Goodwin]

A4 is often an open-collector output on PIC's, it can only sink current, not source it - add a pull-up resistor to make it work more like a normal output. As you are wanting to drive an LED, you could connect the LED and series resistor from the pin to +5V, the LED would then light when the pin is set low. Or, you could connect the LED from A4 to ground, with the series resistor from A4 to +5V - this would then light when the pin was high - but it does waste current when the LED is turned off as the resistor is then directly across the HT rail.