I2CWRITE problem

[Paul]

I have been reading this discussion with interest as I have had a similiar problem to yours.

What I tried to do was to write 32 words in a word array to a 24LC256. Initially my micro was the 18F452, but I have moved over to the 18F4680. Both devices gave the same problem. My line of code was:

DATA var WORD [31]
AA var WORD
I2WR var byte
I2ADDR var WORD

I2CWRITE PORTC.4, PORTC.3, I2WR, I2ADDR, [ STR DATA\32 ], I2C_ERR

I would then read the data back as single words:

I2CREAD PORTC.4, PORTC.3, I2RD, I2ADDR, [ AA ], I2C_ERR


When I read the data back, I would repeatedly read some correct data, a bunch of $FFFF, more correct data, then the data would appear to 'move' and would not be at the designated eprom address. All very strange, but whats more it was repeatable within locations of the device.

The device data sheet specifiies that it can read and write a page of 64 bytes, (32 words).

I over came the problem by writing each word in the word array individually, pausing 5 ms between each word write. Not the best solution but it work. This way wastes 160ms of processing time.

I am still trying to find a way to solve my problem as I really need to write the data block in one hit. I might try using the hardware I2C technique next as I2CWRITE ... [ STR DATA\32] didn't work for me.


Paul.

[Dave]

Paul, I notice that you have only declared 31 WORDS but you are loading the eeprom with 32 BYTES. You can only load individual BYTES into the eeprom even if they are in an array. You would be loading the LOWBYTE of each of the words in the DATA array into the eeprom. Even then, you have only declared 31 words and not 32.

Dave Purola,
N8NTA

[Paul]

Paul, I notice that you have only declared 31 WORDS but you are loading the eeprom with 32 BYTES. You can only load individual BYTES into the eeprom even if they are in an array. You would be loading the LOWBYTE of each of the words in the DATA array into the eeprom. Even then, you have only declared 31 words and not 32.

Dave Purola,
N8NTA

Hi Dave,

That is correct, the 1st element in the array, DATA[0], the second element DATA[1], the 32nd DATA[31].

The STR command counts the elements in an array, [ STR DATA\1] would send element DATA[0]. PBPro knows if I am using WORDS or BYTES and counts them appropriately.

In this section of the PBPro manual, it clearly states that WORD variable arrays can be sent.

Paul.

[Gusse]

Hi Dave,

That is correct, the 1st element in the array, DATA[0], the second element DATA[1], the 32nd DATA[31].

The STR command counts the elements in an array, [ STR DATA\1] would send element DATA[0]. PBPro knows if I am using WORDS or BYTES and counts them appropriately.

In this section of the PBPro manual, it clearly states that WORD variable arrays can be sent.

Paul.

Hi Paul,

Check from manual about Arrays

It is two different things:
- Number of elements (array; 1,2,3,... )
- Location of element (string; 0,1,2,... )

BR,
-Gusse-

[Art]

Just to elaborate on the problem,
The middle part of this video shows the function that writes to EEPROM.
The messages are short because I can only type about 15 letters before
the first one stuffs up.
Each letter requires 6 bytes because they are stored as mono bitmaps,
and there is some lead in space written with zeros.



Art.

[Gusse]

Hi Art,

Couple of things came to my mind:

What is your oscillator speed?
- I didn't see any DEFINE OSC parameter.

Is EEPROM only load in I2C bus?
- Capacitive loading below 400pF per signal line (I2C spec)

How long wires you have between PIC and EEPROM?
- Timing CLK & data (this should not be a problem for I2C)

Write control pin in EEPROM?
- Grounded? Don't know if floating pin could do something like this?

De-coupling of PIC and EEPROM?
- How many caps and sizes

Crosstalk
- Any nearby signals that could cause coupling?

Grounding
- How is the grounding done? Ground bounce due to common impedance with some high current part of the system (Power supply, PIC, etc...).

Errors in write mode seems to be very systematic so it can't be just noise, which is causing the problem.

BR,
-Gusse-

[Dave]

Paul, Yes I understand that the base element number starts at 0 but, you are DECLARING only 31 elements in the array and not 32. Your declaration of the array size has to be the actual number of elements NOT the last element index. RTFM..... Also think about this statement from the manual...(While a single I2CWRITE statement may be used to write multiple bytes at once, doing so may violate the above write timing requirement for serial EEPROMs. Some serial EEPROMS let you write multiple bytes into a single page before necessitating the wait. Check the data sheet for the specific device you are using for these details. The multiple byte write feature may also be useful with I2C devices other than serial EEPROMs that don=t have to wait between writes.) Thats why I always use the page mode.....

Dave Purola,
N8NTA

[Paul]

Hi Paul,

Check from manual about Arrays

It is two different things:
- Number of elements (array; 1,2,3,... )
- Location of element (string; 0,1,2,... )

BR,
-Gusse-

I had read this section of the manual sometime ago, and have obviously forgotten. Thank you Gusse, Art and Dave. It is good to be corrected and shown your error. Even with the change in array declaration, my page write I2C routine still will not work and exhibit the previously described problem. I will look at the physical aspects of the design (hardware), failing that attempt the hardware I2C routine. I have found some examples of code in the forums.

Paul

[Art]

Dave,
I can't really use page write because I only want to write 6 bytes at a time.
The code in the first post only writes zeros, but it isn't really what I want in my application... it's just a simplified code that exhibits the problem.

I'm duplicating the hardware today, so this will be interesting.

[Dave]

Art, Are you accumulating the data or just re-writing the values at the same locations? If you are accumulating the values (data logger style (appending)) then just wait till you have 64,128 or so on (eeprom page dependent) , readings stored in the shadow ram then dump them to the eeprom.

Dave Purola,
N8NTA