PortD on 18f4550 cofig pullup for switches

[Bonxy]

Hi all

I have a 18f4550 and want to have port D as inputs and connect switches to portd.1 - portd.6

I think i need to set portE.7 to enable portD pullups ??? (porte.7 = 1) ???

the switches will be from the portD pin to ground (active low)

I do not want to use external pullup resistors


Any ideas please :-)

[mister_e]

Datasheet have to be your friend.

Step #1: Download the datasheet
http://ww1.microchip.com/downloads/e...Doc/39632D.pdf

Step #2: Go to table 1-3, and there, you discover that weak pull-ups are only available on PORTB

Step #3: make a decision, use external ones, or move on PORTB.

Case you move on PORTB, you go to section 10.2, then you discover

Each of the PORTB pins has a weak internal pull-up. A
single control bit can turn on all the pull-ups. This is
performed by clearing bit, RBPU (INTCON2<7>). The
weak pull-up is automatically turned off when the port
pin is configured as an output. The pull-ups are
disabled on a Power-on Reset.

You could still decide to don't use any pull-up, or pull-down, it's doable, and if your software is properly done, you can even attach 2 push button per I/O (one to vdd, the other to Vss) ... it will work, but a real waste of time IMHO.

[Bonxy]

Hi Steve

I read the datasheet before i post my message :-/, to me the datasheet says that bit7 on port E set the pull-ups for portD on 18f4550 ?.

Anyway, i could use portB,

I want to have switches that can be active low and active high,

can this be done without resistors ?

thx :-)

[Tom@Nottingham]

I have read the data sheet and have set registers as below for 4550
TRISA = %00111111'An 0-4
TRISB = %00011111'An 8-12
TRISC = %00000000'All output
TRISD = %00000000'All output
TRISE = %00000111'An 5-7
ADCON1 = %00000000'A/D channel All
ADCON2 = %10000011'Right justify for 10 bit
INTCON2 = %10000000'Set to disable pullup on An 8-12?

I cannot disable the weak pullups on portb, can someone please show me how this is done, is pbaden involved?

Thanks

[mister_e]

Ouch,mmm well , seems you're totally right, I totally missed that part, my apologies

Each of the PORTD pins has a weak internal pull-up. A
single control bit, RDPU (PORTE<7>), can turn on all
the pull-ups. This is performed by setting RDPU. The
weak pull-up is automatically turned off when the port
pin is configured as a digital output or as one of the
other multiplexed peripherals. The pull-ups are
disabled on a Power-on Reset. The PORTE register is
shown in Section 10.5 “PORTE, TRISE and LATE
Registers”.

PORTE.7=1 ' this will indeed enable pull-up on PORTD

Intcon2.7=1 will disable the pull-ups as per the datasheet. (pdf page 102)

Out of curiosity, why do you say that you're unable to disable the pull-ups? If you read some voltage from them, maybe you read some "parasitic voltage", and If I remember correctly, some of these I/O on PORTB are also set as analog at POR. See ADCON0 (p262)

ADCON0=%00001111 ' turn of all ADCs

You can also trick PORTB adc with the config fuses.

[Bonxy]

Hi Steve,

I always try the datasheets before I post a help request, the only problem with the datasheets is that they are quite technical and confusing to a dabbler like me who only program for fun.

Anyway, I think i got the active low switch working now, the switch is connected to ground and port pin and it works,

BUT, How do I get a switch to work active high now ?,

I connect the switch to +5v and port pin (it trigger the switch once but do not go back low)

how can i get this to work ? any ideas :-)

[Tom@Nottingham]

Thanks for your/and others invaluable help in guiding me along.

The faulty analog inputs an8, an9 and an12 when connected to a pot 0-5v would, when the applied voltage was reduced, indicate the correct voltage until the voltage went down to 1.5v. I then connected a milliamp meter in circuit with the analog input and measured a current of 1.6 ma. After reading the sbc44 manual I now believe these inputs cannot be used as analog inputs but can be used as digital i/o? I do however have 10 analog inputs that work correctly, as I shall be using lm35/ad22100 to measure temperatures, hopefully.

PS I have now succeeded in getting pc vb2005 to usb pic4550 and believe I now understand how it works. Does upgrading to vb2008 express give any problems?

Tom