problems with I2C.... and ideas why dosent work?

[NavMicroSystems]

...can you explain to me what the purpose of a pullup resistor is and why it is needed in this instance.

OK, I'll try it in brief:

A PullUp is required when you have an output pin that is open Drain (or open Collector)
An open collector output is "open" if not set "LOW"
The PullUp pulls this open Pin "HIGH"

The SDA pin on an I2C device is such an open Drain output as it is bi-directional.

Melanie has written an excellent example for the DS1307, see: MN1307.txt

Another thread about RTC's with a lot of useful information can be found here

Take some time to read it from the beginning, you can really learn a lto from it.

[snood]

so would not having the resistors in explain why i'm getting "00" displaying on my LCD for all the values afrer trying to read?

i ask again.... would i be right in just writing "0" for the seconds value in order to initialise it. i figure this cos surely BCD for 0 is %00000000 and the 7th bit is 0 so this should work... right?

Snood

[snood]

could anyone confirm the above.... i kinda need to know quite quickly.

Snood

[Archilochus]

That'll work fine to set bit.7 assuming your I2C write is working properly.
Program the chip and give it a go.

Arch

[snood]

okay, ive added in the pullup resistors, ive ensured everything is connected to the correct things, ive made sure that i am addressing correctly, as far as i can see, i'm doing everything as i should.... now when i try set the time/dats as above and then read it back i get the values "16"

this is also true of the i2C EEPROM i am using on the same bus.

any ideas?

Snood

edit: i just thought that the value 16 is a hex "F" any ideas?

[NavMicroSystems]

Snood,
this is a perfect time to have a look at the datasheet and the examples you have got.

If you are expecting any further assistance post your schematic and code.
(please cut the code down to the minimum required for reading writing the RTC / EEPROM)

But before posting please do some reading!

[snood]

please..... i have read the data sheet over and over again, ive read various places about I2C and i have studied the sample codes that i have been pointed to and still not a clue


TRISB = %11111111

second VAR BYTE
minute VAR BYTE
hour VAR BYTE
day VAR BYTE
date VAR BYTE
month VAR BYTE
year VAR BYTE

ITCDEVICE VAR BYTE
ITCADDRESS VAR WORD

SDA VAR PORTC.4
SCL VAR PORTC.3

ITCDEVICE = $D0
ITCADDRESS = $00

second = 0
minute = 0
hour = 12
day = 2
date = 25
year = 5

I2CWrite SDA, SCL, ITCDEVICE, ITCADDRESS, [second, minute, hour, day, date, month, year]

Pause 500

I2CRead SDA, SCL, ITCDEVICE, ITCADDRESS, [second, minute, hour, day, date, month, year]

at this point i dend the variables to my LCD and what comes up on the screen is "16"

thanks

Snood

edit: it's been suggested to me that as i'm recieving "16" or a single "f" that maybe something is holding the data line up? still clueless other than that