Troubles with I2C_Write

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- 22nd March 2010, 02:56
The Altruist

Troubles with I2C_Write

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?
- 22nd March 2010, 04:17
mackrackit

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?
- 22nd March 2010, 04:25
Darrel Taylor

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.
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- 22nd March 2010, 04:49
The Altruist

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 '//////////////////////////////////////////////////////////////////////////////
- 22nd March 2010, 04:59
mackrackit

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?
- 22nd March 2010, 06:25
The Altruist

Actually, that's something I had not considered.
Let me go do some research, and I'll get back with an answer to that.
- 22nd March 2010, 15:13
Byte_Butcher

Quote:

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. :o

steve
- 22nd March 2010, 15:29
Chris Barron

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
- 23rd March 2010, 01:04
The Altruist

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
- 23rd March 2010, 01:32
The Altruist

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.
- 23rd March 2010, 23:57
The Altruist

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