I need help with i2c memory

[-c3-]

For my senior project we are using a pic16f84. A large part of the project is storing data in a serial memory chip usint i2c. ive spent 5ish hours trying to figure this out. went through data sheets and searched online, still no success. i am confident my circuit is wired correctly. any help would be greatly appriciated.

the memory used currently is microchip's 24AA512, we also have a 24c01 laying around to play with as well.
i have 2 pull up resistors (5.1k) on scl and sda
write protect is grounded

here is my code,

addr var byte
sda var byte
scl var byte
contR con %10100001
contW con %10100000
x var byte 'test data'
sda=PORTB.0
scl=PORTB.1

addr=%00000000
x=3 'test data is the number 3'
pause 100 'pause just for fun'

I2Cwrite sda,scl,contW,addr,[x] 'should write 3 to address 0, right?'
pause 10
I2Cread sda,scl,contR,addr,[x] 'should read the data'
pause 10
serout Portb.2,4,[x] 'displays data on an LCD'


end

Thanks!

[DynamoBen]

Make your addr a word variable, not byte.

Also make sure you assign a value to your addr before the write command.

Example:

Addr=3
I2Cwrite sda,scl,contW,addr,[x] 'should write 3 to address 0, right?'
pause 10

Finally you may want to add DEFINE I2C_SLOW 1 if things are still not working.

Basically if your wired like the manual says and you do the above it works great.

[NavMicroSystems]

Try this:

addr var word
sda var PORTB.0
scl var PORTB.1
cont con %10100000
x var byte 'test data'
addr=%00000000
x=3 'test data is the number 3'

I2Cwrite sda,scl,cont,addr,[x] 'should write 3 to address 0, right?'
pause 10
I2Cread sda,scl,cont,addr,[x] 'should read the data'
pause 10
serout Portb.2,4,[DEC x] 'displays data on an LCD'


end

[DynamoBen]

Also keep in mind if your hoping to see the number three on the LCD you will need to modify your code a bit.

serout Portb.2,4,[DEC x] 'displays ASCII version of data on an LCD'

[-c3-]

Tried that, still nothing. it makes me wonder if there is something with my circuit i am missing...(i think it is right...)

if any one wants to check the wiring (its not messy)
chip pinouts included

http://www.siue.edu/~bluttin/circuit.htm

thanks

the middle chip is the uln2803, its just driving the leds, ive tried it connected, and unconnected.

[-c3-]

Try this:

addr var word
sda var PORTB.0
scl var PORTB.1
cont con %10100000
x var byte 'test data'
addr=%00000000
x=3 'test data is the number 3'

I2Cwrite sda,scl,cont,addr,[x] 'should write 3 to address 0, right?'
pause 10
I2Cread sda,scl,cont,addr,[x] 'should read the data'
pause 10
serout Portb.2,4,[DEC x] 'displays data on an LCD'


end

when i go to compile i get "bad expression" on serout Portb.2,4,[DEC x]
i am using microcode studio.

[DynamoBen]

You are missing the two pull-up resistors that are required.

Try wiring it identical to the Melabs user manual. This is your best shot at getting it to work. I have included the drawing in this post.

[mister_e]

when i go to compile i get "bad expression" on serout Portb.2,4,[DEC x]
i am using microcode studio.

what about serout Portb.2,4,[#x]???

[-c3-]

what about serout Portb.2,4,[#x]???

that compiles, only problem now is i killed my lcd...... needless to say, from now on i will be a little more careful of which voltage supply i am using.... little puffs of smoke are bad....

[-c3-]

You are missing the two pull-up resistors that are required.

Try wiring it identical to the Melabs user manual. This is your best shot at getting it to work. I have included the drawing in this post.

you are talking about the 2 pull up resistors on scl and sda correct? they are there. as far as i can tell the only difference between what i have and your picture is the cap from vdd to ground on pin 14. ill put that in and see what happens..

[DynamoBen]

You may want to wire it exactly like the drawing for testing purposes.

[-c3-]

alright, ive spent some more time on this, with my new lcd. redid the circuit to the schematic posted, still not working for me, it seems it is not writing at all,

do i need to set trisb to something? thats my current line of thought,
thx

[DynamoBen]

Whats not working the LCD or the EEProm?

[mister_e]

Usually you don't need to set TRIS for those built-in command like SERIN/SEROUT/LCDOUT and of course for I2CREAD/I2CWRITE.

For the last, TRIS will change depending if you read ar write from an external I2C device.

What about your whole stuff??? schematic, Parts, Code???

[Darrel Taylor]

I think you should go back up and take another look at Ralph's post.

I know you had an LCD problem at the time, so you may have overlooked it, but it does have 2 important points.

Most important is the declarations of (sda and scl). Originally you had ...

sda var byte
scl var byte
. . .
sda=PORTB.0
scl=PORTB.1

While it may seem that this is assigning PORTB.0 to the sda variable, it doesn't work that way. What it really does is Read PORTB.0 (which is 1 due to the Pull-up resistor) then place the value in sda. Then when you try to use sda, it get's interpreted as a Pin Number (0-15). A 1 as a Pin Number points to PORTB.1

The same goes for scl, so both sda and scl will end up pointing to PORTB.1

The second big point was mentioned by Ben. The address of a 64Kx8 EEPROM has to be a WORD sized variable, not BYTE sized.

A third point that's not as critical, is shown in ralph's example. You only need to have 1 Control Byte. PBP automatically adjusts the value of the control byte depending on whether iit's a Read or a Write operation. The manual specifically says to leave bit 0 "Clear".

Oh yeah, a small typo, it should have been Serout2, that's why you got the compiler error previously.

HTH,
   Darrel

[-c3-]

hey! its working,
the problem i was having was in declaring tris when reading/writing to the memory. ive got it working now and am very happy. thankyou all for the help, heres my current code,

trisb=%00000010 'read i comment one out
'trisb=%00000001 'write
addr var byte
sda var PORTB.0
scl var PORTB.1
cont con %10100000
x var byte 'test data
y var byte 'read data


'x=%00000001 'test data is the number 0'

addr=0
loop:

'I2Cwrite sda,scl,cont,(addr),[x] 'comment out when reading
'pause 20
i2Cread sda,scl,cont,addr,[y] 'should read the data
pause 20
serout portb.2,4,[254,1]

serout Portb.2,4,["y=",#y," x=",#x," a=",#addr] 'visual verification
addr=addr+1
'x=x+%00000001

if addr=255 then end

goto loop

end

[DynamoBen]

I have used external I2C EEProm on a number of projects and have NEVER had to change the TRIS statement to get things to work. Also you STILL have you address variable as a byte, it needs to be a word.

There is still something horribly wrong with either the software or hardware.

[Darrel Taylor]

In your first message, you mentioned 2 different EEPROMs.

24AA512 and 24c01

Which one are you currently having success with?

The 24AA512 is a 64Kx8 device and needs a WORD sized address.
The 24c01 is a 128x8 and only needs a BYTE sized address.

My guess is that you're using the 24c01.

If that's the case, then your test routine loops through 255 address locations, which is double the actual size of the EEPROM. Anything above 127 will loop around and display the first 128 again. Of course, it's just a test routine, but just wanted to let you know.

Best regards,
   Darrel