PIC12F683 pullup problem

Guest · Posted: Fri Jul 18, 2008 9:42 am

Problem with pullup on GP0,GP2,GP3. GP1 is the only pin pulled up.

Ttelmah · Guest

Look at the manual.
Note the first line in the section 'parameters'. 'TRUE', and 'FALSE', _only_applies to parts that have a 'global' pullup (just one instruction to turn them on for the whole port). For parts with the individual bits, you need to use the 'UPMASK' syntax. So:

port_a_pullups(0b00001111);

To turn on the low four pullups.

Best Wishes

Guest · Posted: Fri Jul 18, 2008 2:41 pm

Thanks for reply.

hmmm. On another chip 18F2455 I use the command

Guest · Posted: Fri Jul 18, 2008 2:47 pm

On page 34(REGISTER 4-4: WPU: WEAK PULL-UP REGISTER) in the data sheet there are a description of the pin, is that the same as using port_a_pullups(TRUE); or port_a_pullups(0b00110111)?

Ttelmah · Guest

The 18F2455, only has a _single_ 'pullup enable' bit, that turns on all the pullups. This is the point. 95% of PIC's have the pullups like this. A few have individual pullups, and on these the 'upmask' syntax has to be used. This is what the manual says, if you read the command syntax.
The key is the data sheet. Section 10.2, for the 2455, third paragraph: "A single control bit can turn on all the pullups". On the 12F683 chip, there is instead a bit for each input bit. You turn on just the ones you want. 0b00001111, is to potentially turn on pullups, on GP0, GP1, GP2, and GP3, which is what you asked for, but GP3, does not have a pullup, so the top bit will be ignored. 0b00110111, turns them on for GP0, GP1, GP2, GP4, and GP5.

Best Wishes

Guest · Posted: Fri Jul 18, 2008 3:07 pm

Hi

Thanks for support, your 100% right it work now:-)

Thanks.

sambyte · Joined: 29 Dec 2008 Posts: 12

The code generator, 'PIC Wizard' should have the option to select which bit is to enable/disable rather than just doing the global pullup bit.!!

ckielstra · Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands

I think your suggestion is a welcome extension to the CCS compiler, but... this forum is a User's Forum only. The CCS employees are rarely seen here. Check the message at the top right of this page, bugs (and feature requests) should be emailed to the mentioned address.