I2C with 16F628A mystery

[lilimike]

Hi Steve,

Thank you...!

I tried changing it to 16 and my total is now as expected = 741
and also showing as FF on LCD.

But why should it be 16?
if Dat[0] is working then 0 to 15 = 16 addresses isn't it?


Mike

[mister_e]

an array that range from 0 to 15 is an array of 16 elements... hence the 16. Facile hein?

[lilimike]

Ok that makes sens.

Actually I am feeling kind of stupid right now!
After a glass of wine I will be fine.

Un gros merci!

Mike

[FinchPJ]

Ok that makes sens.

Actually I am feeling kind of stupid right now!
After a glass of wine I will be fine.

Un gros merci!

Mike

BTW you defined I2CAddr as a byte, but treat it as a word (2048) - should be a word.
Peter

[lilimike]

This is an interesting observation, Thank you.

I wonder why it still works though!

Funny how sometimes a programming error is undetected by the compiler and then the program runs with unpredictable results and other times it just works!

Mike

[FinchPJ]

Further investigation has revealed why your checksum still worked.... (sorry for the rather brief earlier reply - it was from my mobile phone!). If we use the following code:

I2CAddr     Var byte
Xray        var byte
Alpha       var byte
I2CAddr2    var byte
I2CDevice   var byte

I2cdevice =160
I2CAddr2 = 0

for i2caddr = 0 to 2048 step 16
    i2cwrite d1,d2,i2cdevice,i2caddr,[$55]
    hserout [hex I2CAddr, " "]
    pause 10
next

This reveals that with i2caddr as a byte, the for/next loop assigns the following values to I2CAddr:
0 10 20 30 40 50 60 70 80 90 A0 B0 C0 D0 E0 F0
then stops (whereas as a word continues up to 800 as expected).
So you are actually only writing to a memory address up to F0, but then reading back gives you the correct checksum. However where are you actually writing to memory? - Well the memory assignment by PBP is sequential in alphabetic order, words first then bytes, and the next byte after I2CAddr is in fact I2CDevice in your code, or in my modification, I2CAddr2, as is seen here:

_Alpha           		EQU	RAM_START + 018h
_I2CAddr         		EQU	RAM_START + 019h
_I2CAddr2        		EQU	RAM_START + 01Ah
_I2CDevice       		EQU	RAM_START + 01Bh
_Xray            		EQU	RAM_START + 01Ch

Now the PBP manual states "The Address size sent (byte or word) is determined by the size of the variable that is used. If a byte-sized variable is used for the Address, an 8-bit address is sent. If a word-sized variable is used, a 16-bit address is sent. Be sure to use the proper sized variable for the device you wish to communicate with."

I suspect this is in fact not correct and looking at the assembler code that PBP generates, in fact I2CWRITE seems to send a word, using I2CAddr, I2CAddr2 as the (word) address in my example, or the case of your code, actually I2CAddr, I2CDevice (=$A0) which is I suspect somewhere other than you intended in memory!
Peter

[lilimike]

Thank you Peter,

I understand the first part of your response but not sure about the second part:

Now the PBP manual states "The Address size sent (byte or word) is determined by the size of the variable that is used. If a byte-sized variable is used for the Address, an 8-bit address is sent. If a word-sized variable is used, a 16-bit address is sent. Be sure to use the proper sized variable for the device you wish to communicate with."

I suspect this is in fact not correct and looking at the assembler code that PBP generates, in fact I2CWRITE seems to send a word, using I2CAddr, I2CAddr2 as the (word) address in my example, or the case of your code, actually I2CAddr, I2CDevice (=$A0) which is I suspect somewhere other than you intended in memory!

I will continue to read it over and over, some times it takes me a few times to understand.

Now again I am running into some mystery and I wish I could understand better...

If I run this code:

i2cdevice =$A0
for i2caddr = 0 to 2048 step 16
    i2cwrite d1,d2,i2cdevice,i2caddr,[$01]:i2caddr = i2caddr + 1:pause 10
    i2cwrite d1,d2,i2cdevice,i2caddr,[$01]:i2caddr = i2caddr + 1:pause 10
    i2cwrite d1,d2,i2cdevice,i2caddr,[$01]:i2caddr = i2caddr + 1:pause 10
    i2cwrite d1,d2,i2cdevice,i2caddr,[$3c]:i2caddr = i2caddr + 1:pause 10
    i2cwrite d1,d2,i2cdevice,i2caddr,[$3c]:i2caddr = i2caddr + 1:pause 10
    i2cwrite d1,d2,i2cdevice,i2caddr,[$3c]:i2caddr = i2caddr + 1:pause 10
    i2cwrite d1,d2,i2cdevice,i2caddr,[$3c]:i2caddr = i2caddr + 1:pause 10
    i2cwrite d1,d2,i2cdevice,i2caddr,[$3c]:i2caddr = i2caddr + 1:pause 10
    i2cwrite d1,d2,i2cdevice,i2caddr,[$3c]:i2caddr = i2caddr + 1:pause 10
    i2cwrite d1,d2,i2cdevice,i2caddr,[$08]:i2caddr = i2caddr + 1:pause 10
    i2cwrite d1,d2,i2cdevice,i2caddr,[$08]:i2caddr = i2caddr + 1:pause 10
    i2cwrite d1,d2,i2cdevice,i2caddr,[$08]:i2caddr = i2caddr + 1:pause 10
    i2cwrite d1,d2,i2cdevice,i2caddr,[$21]:i2caddr = i2caddr + 1:pause 10
    i2cwrite d1,d2,i2cdevice,i2caddr,[$21]:i2caddr = i2caddr + 1:pause 10
    i2cwrite d1,d2,i2cdevice,i2caddr,[$21]:i2caddr = i2caddr + 1:pause 10
    i2cwrite d1,d2,i2cdevice,i2caddr,[$ff]:pause 10
next

Then I read the EPROM with Ponyprog and observed everything as expected.


Then I rewrote my code by changing:

for i2caddr = 0 to 2048 step 16

to

for i2caddr = 0 to 1024 step 16

and the 3 first line I replaced $01 by $ff.

I was expecting to see half of the memory filled with my changes but it got filled all the way to address $7FF:


The more I test the more I get confused!

Mike