In article <20040708140342.04915.00000927@mb-m24.aol.com>, Gary Kato 
<garykato@aol.com> writes
>>I am using parallel I/O ports available in the processor. Do I need
>>pullup resistors to hook SCl and SDA to processor?
>
>I'm not a hardware guy but it looks like you do need pullup resistors on both
>lines. You might try getting a book like "Designing Embedded Hardware".

SCL and SDA lines do need pullups, stick a 4K7 up to the positive supply 
on each one. Even if the processor already has pullups it won't do any 
harm
-- 
Tim Mitchell

>I am using parallel I/O ports available in the processor. Do I need
>pullup resistors to hook SCl and SDA to processor?

I'm not a hardware guy but it looks like you do need pullup resistors on both
lines. You might try getting a book like "Designing Embedded Hardware".

learner wrote:
> garykato@aol.com (Gary Kato) wrote in message news:<20040708061902.04622.00000970@mb-m10.aol.com>...
> 
>>>Is it possible to hook pins SCL,SDA of Dallas DS1307 RTC with I/O
>>>ports of Intel 386EX processor?
>>
>>I don't think there's any hardware reason why you couldn't do that and drive
>>the I2C protocol via pure software. I assume you mean regular digital I/O pins
>>and not to anything like a UART.
> 
> 
> I am using parallel I/O ports available in the processor. Do I need
> pullup resistors to hook SCl and SDA to processor? I am new to this
> field and any help will be appreciated.
> 
> Thanks

What might be a problem is the open-drain nature (wire-and) of the
I2C bus. On many I/O ports, you'll need three-state buffers and
send the data via the output enable pin to simulate an open-drain
device.

If the output bits are easily individually controlled as inputs
or outputs, the same effect can be created using the data direction
register as the outputs and pre-set the output register bits to zeroes.

You have to create the bus sequences bit by bit in software.

HTH

Tauno Voipio
tauno voipio @ iki fi

garykato@aol.com (Gary Kato) wrote in message news:<20040708061902.04622.00000970@mb-m10.aol.com>...
> >Is it possible to hook pins SCL,SDA of Dallas DS1307 RTC with I/O
> >ports of Intel 386EX processor?
> 
> I don't think there's any hardware reason why you couldn't do that and drive
> the I2C protocol via pure software. I assume you mean regular digital I/O pins
> and not to anything like a UART.

I am using parallel I/O ports available in the processor. Do I need
pullup resistors to hook SCl and SDA to processor? I am new to this
field and any help will be appreciated.

Thanks

>Is it possible to hook pins SCL,SDA of Dallas DS1307 RTC with I/O
>ports of Intel 386EX processor?

I don't think there's any hardware reason why you couldn't do that and drive
the I2C protocol via pure software. I assume you mean regular digital I/O pins
and not to anything like a UART.