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

[snood]

okay, i'm using a PIC16F876A and a DS1307 RTC, i have written a short program which should set the time, then loop reading the time to confirm that it is infact set. the problem is when i go to run this in the device... the LCD screen just shows up values with everything reading "00". this to me suggests that i have something wrong with the write commands. here's the offending code:


TRISC = %11111111
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 byte

SDA var PORTC.4
CLK Var PORTC.3

LCDOUT var PORTB.0

ITCDEVICE = $D0
ITCADDRESS = $00

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

pause 1000

I2CWRITE SDA, CLK, ITCDEVICE, ITCADDRESS, [second, minute, hour, day, date, year]

second = 255 'change variables to make sure it recieves correctly'
minute = 255
hour = 255
day = 255
date = 255
year = 255

loop:

pause 500

I2CREAD SDA, CLK, ITCDEVICE, ITCADDRESS, [second, minute, hour, day, date, year]

serout LCDout, 6,[254,1] 'clears screen'
serout LCDout, 6,[254,128] 'sets position'
serout LCDout, 6,[#hour,":",#minute,":",#second] 'displays the read time
serout LCDout, 6,[254,192] 'next line'
serout LCDout, 6,["month:",#month," year:",#year] 'displays the read date

goto loop

[@sda]

Spelling mistake?
SCL instead of SLK for the I2C variable.

sda

[Archilochus]

Hi snood,
Isn't "LCDOUT" a reserved word in PBP? Don't know if that might cause problems.

Arch

[snood]

Hi snood,
Isn't "LCDOUT" a reserved word in PBP? Don't know if that might cause problems.

Arch

well i have just actually re-written that for the purpose of the forum, i dont currently have access to my one with the problem... LCDOUT is just what i called it here, it's called "screen" on my actual version, either way, it's not the screen i'm having trouble with, thats working fine, it's just not displaying the "correct" information from the RTC.. i just read in another post something about when the DS1307 is brand new you have to do something to it to make it work, can someone explain this to me? as the above code is being run on a fresh 1307.

thankyou

Paul

[NavMicroSystems]

Snood,

if you search the Forum for "DS1307" you'll find a number of examples.
(be honest, you haven't really searched)

Do you have 4k7 Pullup Resistors on SDA and SCL ?

For additional Information see: DataSheet

[snood]

ogg dear i never noticed the 4k7 resistor... how vital is this to have? i connect the resistor to the SDA only according to the datasheet, what does the other end of the resistor connect to? +5v?

and yes ive searched for 1307.

paul

[Archilochus]

Hi Snood,
Ohh... yeah, those pullups are important! Hook them from the SDA and SCL lines to your positive rail that powers the PIC and 1307.

Here's a bit from the data sheet about starting up a 'new' 1307:

"Bit 7 of register 0 [seconds] is the clock halt (CH) bit. When this bit is set to a 1, the oscillator is disabled. When cleared to a 0, the oscillator is enabled."

Since you set 'seconds' to 0, the clock should be enabled, assuming the the I2C write command is working properly.

Arch

[NavMicroSystems]

ogg dear i never noticed the 4k7 resistor...

No pullUp, No Success

what does the other end of the resistor connect to? +5v?

what else could you connect a PulUp to?

...and yes ive searched for 1307.

Well, then everything should be pretty clear.
(if you have taken the time to read through the threads)