I2C CONFUSION, Help needed please

[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

[FromTheCockpit]

Checked it. It fails on the first write statement.

[FromTheCockpit]

Fails on the second statement if I swap the values of Addr. i.e. First $37, second Addr $36. First one goes fine.

[LinkMTech]

Checked it. It fails on the first write statement.

Okay let's fix that first.
Put brackets around the Loc as shown in the PBP manual to see if that helps.

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

[FromTheCockpit]

I did exactly the same as above and the sequence completed fine. BUT the values are not consistent with the datasheet, I should get '$2E' from location 0, but WHATEVER location I try to read, I am getting '$FF'

[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.

[FromTheCockpit]

Success but with one question.
Finally, I put 20MHz clock. It started working with absolutely no problems.

This leaves me with one MAJOR question - Is there any way, I can run the whole show at 4MHz, any settings I missed or anything I can do. I have got no extra pins on my PIC to put an external oscillator, I want to confirm the answer to this question before I start again and choose another suitable PIC. My task will get much much easier if there is a way to run it at 4 Sweet Megahertz.

Many many many thanks to you guys for trying to helping me out on this. This forum is the best.

[Demon]

16F688 can go up to 8MHz on internal oscillator.

I'd try that before changing PIC.

Robert

[LinkMTech]

I put a test circuit together on my LAB-X4 using the PIC16F688 to talk to a 128kB FRAM.
I could feel your pain when trying to make your test program work so decided to start from almost scratch.
The TRIS statements were missing some bit assignments which are not a good thing, from what I read somewhere here by Henrik Olssen, so I put them in.
The order of CONFIG's and other setups were rearranged as well. Not really sure which fixed it but,

The end results were that it works at 4MHz and here's the program to compare with.

'
' This setup uses a PIC16F688 and a FM24V01, 128kB Nonvolatile RAM to test
' the I2CREAD/WRITE functions at 4MHz.
' 
' First: The FRAM memory is loaded with values 1~5 starting from 
' location 0 using Word size address. The values written are sequentially
' loaded into the next memory location, so only the starting address is 
' needed for this test.
' Read address = $A0
' Write address = $A1
'
' Second: The FRAM memory locations 0 thru 4 are READ in a loop then stops
' and waits the Test button on the LAB-4X to be pushed and repeats.
'
' The data was monitored with the Saleae Logic scope.
' Max clock speed measured at 4Mhz was 29kHz
'
' The DEBUG function was not used during this test
'****************************************************************

#CONFIG
ifdef PM_USED
device pic16F688, intrc_osc_noclkout, wdt_on, mclr_on, protect_off
else
__config _INTRC_OSC_NOCLKOUT & _WDT_OFF & _PWRTE_ON & _MCLRE_OFF & _CP_OFF & _CPD_OFF & _BOD_OFF & _IESO_OFF & _FCMEN_OFF
endif
#ENDCONFIG

'-----------------------------------------------------
PORTA=0
PORTC=0
TRISA = %00001000   ' All 8 bits assigned one way or the other
TRISC = %00000000   ' All 8 bits assigned one way or the other
CMCON0 = 7
ANSEL = 0
OPTION_REG = 128    ' PORTA pullups disabled
INTCON=128
OSCCON = %01100001  ' Oscillator set to 4MHz

DEFINE DEBUG_REG PORTC
DEFINE DEBUG_BIT 3
DEFINE DEBUG_BAUD 2400
DEFINE DEBUG_MODE 1
DEFINE OSC 4
Include "modedefs.bas"
 
'-----------------------------------------------------------
Value       VAR BYTE
WR_Addr     VAR BYTE
RD_Addr     VAR BYTE
LOC         VAR WORD    ' FRAM address must be sent as Word size
x           VAR BYTE
'------------------------------------------------------------
SCL     VAR PORTA.4     ' RA4, pin #3
SDA     VAR PORTA.5     ' RA5, pin #2
Change  VAR PORTA.3     ' Push button on LAB-X4
LED     VAR PORTA.0     ' Test LED. LOW = ON
'------------------------------------------------------------
LOC = 0             ' Start at 0
LED = 1             ' Turn LED OFF
PAUSE 1000          ' Give me a chance to start the monitor

GOSUB Load_Mem      ' Load FRAM memory locations 0~4 with values 1~5 

Main:   
    FOR LOC = 0 TO 4
        LED = 0     ' Turn ON LED, scope monitored 
        I2CWRITE SDA,SCL,$A0,[LOC],Fail1
        PAUSEUS 25  ' Paused to see on display
        I2CREAD SDA,SCL,$A1,[VALUE],Fail2
        PAUSEUS 500 ' Paused to seperate packets, viewing purpose only
        LED =1      ' Turn OFF LED
    NEXT LOC

WHILE CHange: WEND  ' Wait until button pushed
PAUSE 500           ' Cheap debounce
GOTO Main

'----------------------- Fail routines -------------------------------

Fail1:					' Try Write again
	FOR x=0 to 50
		LOW LED : PAUSE 50 : HIGH LED : PAUSE 50
	Next x
GOTO Main

Fail2:					' Try read again
	For x=0 to 5
		LOW LED : PAUSE 250 : HIGH LED : PAUSE 250
	Next x
GOTO Main

'---------------------- Load FRAM --------------------------------------

Load_Mem:
    LED = 0     ' Turn ON LED, scope monitored 
    I2CWRITE SDA,SCL,$A0,[LOC,1,2,3,4,5],Fail1
    LED = 1     ' Turn OFF LED
RETURN    
        
END

This first screenshot is from:

Load_Mem:
    LED = 0     ' Turn ON LED, scope monitored 
    I2CWRITE SDA,SCL,$A0,[LOC,1,2,3,4,5],Fail1
    LED = 1     ' Turn OFF LED
RETURN

The 2nd and 3rd from the first and last loop Reads showing the values 1 and 5 after the $A1 READ address.