Troubles with I2C_Write

**The Altruist** · - 22nd March 2010, 02:56

I'm trying to send an I2C message to a non-EEPROM. Now everyone may laugh and say "So what's the problem?"
Every I2C example I've seen written is for EEPROMs. The I2C_WRITE command seems built around them.

The complicating part is the EEPROM address BYTE. That may seem odd, but I have a good reason. I'm not sending an address byte. I'm just sending pure data. In this case, I'm sending it to an I2C-driven DAC.

Right now, I'm using this method and nothing is working.

'Assuming 'result' is a word variable containing a 10-BIT value shifted left twice with 4 bits of empty header (per the DAC datasheet):
'So it looks like 0000xxxx-xxxxxx00

I2CWRITE PORTB.1, PORTB.4, $9C, result.HIGHBYTE, [result.LOWBYTE]

I'm using PBP 2.5, an ICD2, a PIC16F819, and a DAC101C085.

Any suggestions?

**mackrackit** · - 22nd March 2010, 04:17

Here is an example with a RTC
http://www.picbasic.co.uk/forum/showthread.php?t=12671

But the problem might be with the placement of the [ ]

Showing your whole code may also help. Where is the data coming from?

**Darrel Taylor** · - 22nd March 2010, 04:25

In the manual, there are small clues that take some getting used to.

I2CWRITE DataPin,ClockPin,Control,{Address,}[Value{,Value...}]{,Label}

The curly braces around Address means it's optional.

If you don't need to send an address, leave it out.
Then put the HIGHBYTE data inside the square brackets.
<br>

**The Altruist** · - 22nd March 2010, 04:49

This is a trimmed down version of my code. And frankly, nothing is working. I'm not a hardware guy, so I can't tell if my setup is wired wrong. The guy I work with put it together for me. He's a professional so I'm not going to doubt him. But something, somewhere, isn't working.

Code:

;@   __CONFIG    _HS_OSC & _WDT_OFF

DEFINE  OSC 20
DEFINE	ADC_BITS	10			'10-bit ADC
DEFINE	I2C_SLOW		1

' Define used register flags
SSPIF   VAR     PIR1.3          ' SSP (I2C) interrupt flag
BF      VAR     SSPSTAT.0       ' SSP (I2C) Buffer Full
R_W     VAR     SSPSTAT.2       ' SSP (I2C) Read/Write
D_A     VAR     SSPSTAT.5       ' SSP (I2C) Data/Address
CKP     VAR     SSPCON.4        ' SSP (I2C) SCK Release Control
SSPEN   VAR     SSPCON.5        ' SSP (I2C) Enable
SSPOV   VAR     SSPCON.6        ' SSP (I2C) Receive Overflow Indicator
WCOL    VAR     SSPCON.7        ' SSP (I2C) Write Collision Detect
ADCGO	VAR		ADCON0.2 		' ADC GO /DONE bit: High to start. Automatically goes low when finished.


' Define constants
I2Caddress	CON	$12 * 2			' Make our address twice the actual address (bit shifted left)
BUFFERSIZE	CON	$10				' 16 Word addresses
BUFFERTOP	CON  BUFFERSIZE - 1	' Top of Buffer
DATASIZE	CON	20


' Allocate RAM
modLevel	VAR		WORD[BUFFERSIZE]' Modulation Level                      '32
dataout		VAR     BYTE[2]			' Data out array                        '18
result		VAR		WORD			' ADC result                            '2
Counter     VAR		BYTE			' Counter for Arrays                    '1
Iter    	VAR		BYTE			' Generic Iterator						'1
compHi		VAR		WORD            ' Comparison Hi Value                   '2
compLo		VAR		WORD            ' Comparison Lo Value                   '2
TempWord	VAR		WORD			' Swap Variable



' Initialize ports and directions
		ADCON0 = $81			' Clock /32
        ADCON1 = $81			' PORTA.0 analog
'        TRISB.1 = 1				' Pin for SDA
'        TRISB.4 = 1				' Pin for SCL
        TRISB.1 = 0				' Pin for SDA
        TRISB.4 = 0				' Pin for SCL
		
        TRISA.2	= 1				' Pin RA.2 for AN2
		TRISA.3	= 0
		TRISA.4	= 0

mainloop:						' Main program loop
'/////////////////////////////////////////////////////////////////////////////
'This is the portion I'm testing out
'\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
		result =	512
		result = result << 2
		I2CWRITE PORTB.1, PORTB.4, $9C, [result.HIGHBYTE, result.LOWBYTE]	



loopforfun:
	GOTO	loopforfun
'//////////////////////////////////////////////////////////////////////////////

**mackrackit** · - 22nd March 2010, 04:59

You say nothing is working. Is there a LED on board that can be made to blink to see if the chip is even running?

This line bothers me

Code:

;@   __CONFIG    _HS_OSC & _WDT_OFF

I take it you are using the default in the inc file?

**The Altruist** · - 22nd March 2010, 06:25

Actually, that's something I had not considered.
Let me go do some research, and I'll get back with an answer to that.

**Byte_Butcher** · - 22nd March 2010, 15:13

Originally Posted by The Altruist

And frankly, nothing is working. I'm not a hardware guy, so I can't tell if my setup is wired wrong. The guy I work with put it together for me. He's a professional so I'm not going to doubt him. But something, somewhere, isn't working.

Since someone else built the hardware for you, check and make sure that there is a resistor to pull MCLR high.

I just wasted a big chunk of my weekend trying to figure out what configuration fuses and register(s) weren't configured right on a "new to me" chip.
Turned out I forgot to pull MCLR high, so the chip wasn't running at all.

steve

**Chris Barron** · - 22nd March 2010, 15:29

Do you have appropriate pullup resistors on the I2C clock and data lines ?
I have seen values from 1.2k to 10k work to good effect. The lower the value the less susceptible the signals are to noise

**The Altruist** · - 23rd March 2010, 01:04

Hm.... false alarm. The DAC chip was bad.
We have it (or at least a simple saw tooth wave demo) working now:

Code:

;@   __CONFIG    _HS_OSC & _WDT_OFF

DEFINE  OSC 20
DEFINE	I2C_SLOW		1




' Allocate RAM
result		VAR		WORD			' ADC result                            '2
Iter    	VAR		BYTE			' Generic Iterator						'1


' Initialize ports and directions
        TRISB.1 = 0				' Pin for SDA
        TRISB.4 = 0				' Pin for SCL
		

mainloop:						' Main program loop
		'This should set the DAC to output.
		FOR ITER =0 TO 254
		result = ITER
		result=result<<4
		PAUSE	100
		I2CWRITE PORTB.1, PORTB.4, $9C, [result.HIGHBYTE, result.LOWBYTE]
		NEXT
		FOR ITER =255 TO 1 STEP -1
		result = ITER
		result=result<<4
		PAUSE	100
		I2CWRITE PORTB.1, PORTB.4, $9C, [result.HIGHBYTE, result.LOWBYTE]
		NEXT
		goto mainloop

**The Altruist** · - 23rd March 2010, 01:32

While I have your attention, I'm puzzling over how to efficiently do a 10-bit by 10-bit division (which will yield a value 0<x<1) then multiply it again by 1023 to get a number (0<=x<=1023). I'd prefer not to use LONG values as they eat up precious RAM, but I also want to keep it reasonably quick. I have plenty of words set up, but no LONGs.
Here's the math:
a, b, and x are WORDs
x=1023*(a-b)/(a+b)
Any thoughts?
EDIT: Oh. Ha ha. I don't even have LONGs to work with. Yeah... that makes a difference now, doesn't it?
The only thing I can conceive of is using a two-fold mechanism that combines this:

Code:

'Shift RESULT left 10 times
FOR Iter=1 to 10
	RESULT=RESULT<<1
NEXT

with this:

Code:

'RESULT= B / A
RESULT=0
WHILE B>A
	B=B-A
	RESULT=RESULT+1
WEND

The trick is to keep the working value inside 16-bits, but inside 10 bits at the very end.

**The Altruist** · - 23rd March 2010, 23:57

For those of you wondering, this algorithm gives decently accurate 10-bit ratios with a Big O of (n^2). I hope some one finds it useful.
Bear in mind that the Numerator MUST be smaller than the Denominator, and that the denominator bit-shifted left to be bigger than the Power of 2 you're trying to fit it in. Therefore, don't change the 1024 to 16384 and expect it to work (while still using 16-bit WORDs).

Code:

TenBitRatio:
		Result=0
		while Denominator<1024 
			Numerator=Numerator<<1
			Denominator=Denominator<<1
		WEND
		while	Denominator>0
			Digit=0
			while	Numerator>Denominator
				Numerator	=	Numerator	-	Denominator
				Digit=Digit+1
			WEND
			Denominator	=	Denominator>>1
			Result	=	Result	<<	1
			Result	=	Result	+	Digit
		WEND

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