CCS C Software and Maintenance Offers
FAQFAQ   FAQForum Help   FAQOfficial CCS Support   SearchSearch  RegisterRegister 

ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

CCS does not monitor this forum on a regular basis.

Please do not post bug reports on this forum. Send them to CCS Technical Support

Pull up resistor

 
Post new topic   Reply to topic    CCS Forum Index -> General CCS C Discussion
View previous topic :: View next topic  
Author Message
Guest








Pull up resistor
PostPosted: Thu Nov 26, 2009 11:12 am     Reply with quote

I want to know the pins of pic18f250 and 18f2550 requires external pull up resistors


I know RA4 need one, but what about other pins.




Thanks
John P



Joined: 17 Sep 2003
Posts: 331

View user's profile Send private message

PostPosted: Thu Nov 26, 2009 11:52 am     Reply with quote

Huh. Difficult problem. What did you find when you read the manual?
Guest








PostPosted: Thu Nov 26, 2009 12:23 pm     Reply with quote

r u jocking...
bkamen



Joined: 07 Jan 2004
Posts: 1615
Location: Central Illinois, USA

View user's profile Send private message

PostPosted: Thu Nov 26, 2009 12:26 pm     Reply with quote

Probably not.

The Datasheet for any PIC processor (barring doc errors) will tell you everything you need to know.

You want to look in the section for I/O Ports.

Cheers,

-Ben
_________________
Dazed and confused? I don't think so. Just "plain lost" will do. :D
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

View user's profile Send private message

PostPosted: Thu Nov 26, 2009 12:39 pm     Reply with quote

To find this information, look in the PIC's data sheet, in the
Device Overview section. Look at the pinout tables in that section:
Quote:
TABLE 1-2: PIC18F2455/2550 PINOUT I/O DESCRIPTIONS

If an i/o pin says "Open Drain" in the description, it means that the pin
can only be set to a low level. The PIC can't drive it high.
If you want the pin to have the ability to go to a high level, then you
must add an external pull-up resistor to it. Then call the output_float()
function and the pull-up resistor will take it to a high level.

A typical description for an Open Drain pin in the Overview section will
look like this:
Quote:
Output is open drain type.

or this
Quote:
Open drain when configured as output.

Notice that the 18F2550 does not have that description for pin RA4.
Guest








PostPosted: Thu Nov 26, 2009 3:08 pm     Reply with quote

PCM programmer wrote:
To find this information, look in the PIC's data sheet, in the
Device Overview section. Look at the pinout tables in that section:
Quote:
TABLE 1-2: PIC18F2455/2550 PINOUT I/O DESCRIPTIONS

If an i/o pin says "Open Drain" in the description, it means that the pin
can only be set to a low level. The PIC can't drive it high.
If you want the pin to have the ability to go to a high level, then you
must add an external pull-up resistor to it. Then call the output_float()
function and the pull-up resistor will take it to a high level.

A typical description for an Open Drain pin in the Overview section will
look like this:
Quote:
Output is open drain type.

or this
Quote:
Open drain when configured as output.

Notice that the 18F2550 does not have that description for pin RA4.


Thanks u for your reply
Guest








PostPosted: Thu Nov 26, 2009 3:12 pm     Reply with quote

one more doubt

Quote:
Selection of any I2C mode with the SSPEN bit set
forces the SCL and SDA pins to be open-drain,
from data sheet

what it means...

I am not using I2C mode...Is there any need of pull-up resistors ..
Ttelmah
Guest







PostPosted: Thu Nov 26, 2009 3:58 pm     Reply with quote

Basically no, but it depends what you are actually doing with the pin.

So (for instance), if you are using a pin as an input, and want it to float to a 'known' level, then pull-ups are needed.
Similarly, if using I2C, then they are needed.
Similarly, if you want to implement your own 'wire-or' strategy, then pull-ups become needed.
If you need to ensure that a pin when 'high', goes to a higher level than the data sheet warrants a output to drive 'up' to, then pull-ups are needed (common when driving some types of 5v logic from 3.3v chips).
A few pins (A4, on some PICs), do not have an internal high drive ability.
In each case, the data sheet shows the drive capabilities and levels involved.

If you are using a normal pin as a conventional output, then, 'no'.

Best Wishes
Display posts from previous:   
Post new topic   Reply to topic    CCS Forum Index -> General CCS C Discussion All times are GMT - 6 Hours
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group