I2C CONFUSION, Help needed please

[LinkMTech]

> It is bit 7 for R/W (Slave address + write bit)

How did you find that?

[FromTheCockpit]

Picked up from the datasheet of the device. That is what I understood, am I wrong?
Though I did tried $3B & $5B.

[LinkMTech]

Not sure if you're wrong or not. I'm still trying to decipher that part in the datasheet because they don't make it easy. I've found that some information has to be gleaned from other devices of the same manufacturer to put the whole story together, kinda sucks!

I also noticed the address stays at $1B after the first loop in your test program and if it works you might miss it.

Note: I just found one of my programs on another I2C device that has bit 1=0 as the Write bit.
$1B = $00011011 used for Read
$1A = $00011010 used for Write

[FromTheCockpit]

I read it again to confirm this, the attachment is my source. It also mentions 9 bits long address. Not sure who sends an ack. I see that in read statement the device send ack, so why add it to the address PIC is sending. Very confusing.

[LinkMTech]

Ahhhh... okay
Let's use this info then. Looks like the address is using bits 1~7 and the Read/Write control bit is 0.
If control bit is set (=1) then Read, if bit cleared (=0) then Write

So:
%00110111 = $37 ' Read function
%00110110 = $36 ' Write function

Try that.

By the way, the device sends the ACK, or acknowledges, by holding the Data line LOW on the 9th clock cycle. The PIC will see this and continue to send data.

[FromTheCockpit]

By the way, the device sends the ACK, or acknowledges, by holding the Data line LOW on the 9th clock cycle. The PIC will see this and continue to send data.

How do I implement this, like this below?

Main:
High Led : Pause 500: Low Led : PAUSE 500
	Addr=$36
	I2CWRITE SDA,SCL,ADDR,LOC
	Addr=$37 : pause 10                    ' OR If SDA=1 then main 
	I2CREAD SDA,SCL,loc,[VALUE],Fail
	PAUSE 25
	DEBUG  HEX Value,13,10
	PAUSE 250
	DEBUG "Done....",13,10
WHILE 1 : WEND
Goto Main

Fail:
	toggle portc.2
goto main

[LinkMTech]

Just notice the address missing on the Read function.
Moved the Fail label after Write to test this part first. This will let you know if the Write address was recognized so the Pause 10 is not needed.

Main:
High Led : Pause 500: Low Led : PAUSE 500
	Addr=$36
	I2CWRITE SDA,SCL,ADDR,LOC, Fail  ' Test here first
	Addr=$37 ': pause 10                    ' OR If SDA=1 then main 
	I2CREAD SDA,SCL,ADDR,loc,[VALUE] ',Fail
	PAUSE 25
	DEBUG  HEX Value,13,10
	PAUSE 250
	DEBUG "Done....",13,10
WHILE 1 : WEND
Goto Main

Fail:
	toggle portc.2
goto main

[Demon]

...
%00110111 = $37 ' Read function
%00110110 = $36 ' Write function
..

I would have thought:
%00000001 = $37 ' Read function
%00000000 = $36 ' Write function

I don't see in this datasheet where you get the rest.

Robert

[FromTheCockpit]

I just discovered, that the I am actually receiving only 1 byte as expected. Rest are just "Start......"13,10 and "Done",13,10. Yesterday got too exhausted and missed this mistake of mine.

Here is the current code with

Start:
Loc=0

Start_Again:
	I2CWRITE SDA,SCL,$36,[LOC],Fail1

Main:
	Value=0
	High Led : Pause 500: Low Led : PAUSE 500
	I2CREAD SDA,SCL,$37,[VALUE] ,Fail2
	PAUSE 250
	DEBUG  Value
	Loc=Loc+1
	If Loc<4 then Start_Again		' Read first 4 locations
	x=0

WHILE !Change			' Stay here if Change Stays High
		 Pause 500  : x=x+1
		If x =10 then 
			LOC=3 : Goto Main ' Do another read
		Endif			
WEND
while Change : pause 100 : wend	' Stay here if change is Low
Goto Start

Fail1:					' Try Write again
	For x=0 to 50
		High Portc.2 : Pause 50 : Low PortC.2 : Pause 50
	Next x
Goto Start_again

Fail2:					' Try read again
	For x=0 to 5
		High Portc.2 : Pause 250 : Low PortC.2 : Pause 250
	Next x
Goto Main

Every time Change line goes low (detected something), I try to read first 4 memory locations. The communication fails a lot of times (both write and read (write more than read) )in this attempt but I do get the data on the screen finally. Secondly, the data which comes is wrong. For example, memory locations 0 does not read 2E for a start.