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MSP430G2335 Interfacing with a DS1307


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For the past 4 hours I've been trying to troubleshoot a I2C communication between my MSP430G2335 and a DS1307 (powered from a external 5V PSU). This is the code I'm using (it uses alanbarr I2C library):

#include <msp430g2553.h>
#include "i2c.h"

void main() {
	WDTCTL = WDTPW + WDTHOLD;  // Disable WDT.
	BCSCTL1 = CALBC1_1MHZ;     // 1MHz clock.
	DCOCTL = CALDCO_1MHZ;
	BCSCTL2 &= ~(DIVS_3);      // SMCLK = DCO = 1MHz.


	i2cSetupPins();//0x68
	i2cSetupTx(0x68);
	i2cTransmit(0, 1);
	i2cSetupRx(0x68);
	char t[100];
	i2cReceive(t, 1); // Nothing. Just for testing.
}

The problem is that all I get is this:

ST5C78q.png

 

Then apparently the CPU hangs (since nothing happens). So, anyone got any idea why that's happening? (by the way, yes, I have the 10k pullup resistors)

 

PS: It's 2am and I just rage quitted this, so you guys are my last hope.

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One thinf i had to put in my code was a timeout fail because it would hang. If the slave module doesnt send ack bits consistently, the module can get confused and depending on how the code is written it will hang waiting for an event thats not gonna happen

 

Btw, based on your sda trace, there is no ack bit being sent (since the line is high until the stop command is sent)

 

Check your wiring, make sure its good

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Please refer to this thread Problem with I2C RTC DS1307 Module at http://forum.43oh.com/topic/3872-problem-with-i2c-rtc-ds1307-module/

 

The DS1307 works at 5V while the MSP430 is 3.3V-based.

 

Add logic level converters or consider instead the 3.3V-based NXP PCF2129A. And check pull-up resistors.

 

Remember, the search box on this forum works very well :smile:

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