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MSP430 I2C Slave
//******************************************************************************
// MSP430G2x21/G2x31 Demo - I2C Slave Receiver, single byte
//
// Description: I2C Slave communicates with I2C Master using
// the USI. Master data should increment from 0x00 with each transmitted byte
// which is verified by the slave.
// LED off for address or data Ack; LED on for address or data NAck.d by the slave.
// ACLK = n/a, MCLK = SMCLK = Calibrated 1MHz
//
// ***THIS IS THE SLAVE CODE***
//
// Slave Master
// (msp430g2x21_usi_07.c)
// MSP430G2x21/G2x31 MSP430G2x21/G2x31
// ----------------- -----------------
// /|\| XIN|- /|\| XIN|-
// | | | | | |
// --|RST XOUT|- --|RST XOUT|-
// | | | |
// LED <-|P1.0 | | |
// | | | P1.0|-> LED
// | SDA/P1.7|<-------|P1.7/SDA |
// | SCL/P1.6|<-------|P1.6/SCL |
//
// Note: internal pull-ups are used in this example for SDA & SCL
//
// D. Dang
// Texas Instruments Inc.
// October 2010
// Built with CCS Version 4.2.0 and IAR Embedded Workbench Version: 5.10
//******************************************************************************
#include <msp430g2221.h>
char MST_Data = 0; // Variable for received data
char SLV_Addr = 0x90; // Address is 0x48<<1 for R/W
int I2C_State = 0; // State variable
void main(void)
{
WDTCTL = WDTPW + WDTHOLD; // Stop watchdog
if (CALBC1_1MHZ ==0xFF || CALDCO_1MHZ == 0xFF)
{
while(1); // If calibration constants erased
// do not load, trap CPU!!
}
BCSCTL1 = CALBC1_1MHZ; // Set DCO
DCOCTL = CALDCO_1MHZ;
P1OUT = 0xC0; // P1.6 & P1.7 Pullups
P1REN |= 0xC0; // P1.6 & P1.7 Pullups
P1DIR = 0xFF; // Unused pins as outputs
P2OUT = 0;
P2DIR = 0xFF;
USICTL0 = USIPE6+USIPE7+USISWRST; // Port & USI mode setup
USICTL1 = USII2C+USIIE+USISTTIE; // Enable I2C mode & USI interrupts
USICKCTL = USICKPL; // Setup clock polarity
USICNT |= USIIFGCC; // Disable automatic clear control
USICTL0 &= ~USISWRST; // Enable USI
USICTL1 &= ~USIIFG; // Clear pending flag
_EINT();
while(1)
{
LPM0; // CPU off, await USI interrupt
_NOP(); // Used for IAR
}
}
//******************************************************************************
// USI interrupt service routine
//******************************************************************************
#pragma vector = USI_VECTOR
__interrupt void USI_TXRX (void)
{
if (USICTL1 & USISTTIFG) // Start entry?
{
P1OUT |= 0x01; // LED on: sequence start
I2C_State = 2; // Enter 1st state on start
}
switch(I2C_State)
{
case 0: // Idle, should not get here
break;
case 2: // RX Address
USICNT = (USICNT & 0xE0) + 0x08; // Bit counter = 8, RX address
USICTL1 &= ~USISTTIFG; // Clear start flag
I2C_State = 4; // Go to next state: check address
break;
case 4: // Process Address and send (N)Ack
if (USISRL & 0x01) // If read...
SLV_Addr++; // Save R/W bit
USICTL0 |= USIOE; // SDA = output
if (USISRL == SLV_Addr) // Address match?
{
USISRL = 0x00; // Send Ack
P1OUT &= ~0x01; // LED off
I2C_State = 8; // Go to next state: RX data
}
else
{
USISRL = 0xFF; // Send NAck
P1OUT |= 0x01; // LED on: error
I2C_State = 6; // Go to next state: prep for next Start
}
USICNT |= 0x01; // Bit counter = 1, send (N)Ack bit
break;
case 6: // Prep for Start condition
USICTL0 &= ~USIOE; // SDA = input
SLV_Addr = 0x90; // Reset slave address
I2C_State = 0; // Reset state machine
break;
case 8: // Receive data byte
USICTL0 &= ~USIOE; // SDA = input
USICNT |= 0x08; // Bit counter = 8, RX data
I2C_State = 10; // Go to next state: Test data and (N)Ack
break;
case 10:// Check Data & TX (N)Ack
USICTL0 |= USIOE; // SDA = output
if (USISRL == MST_Data) // If data valid...
{
USISRL = 0x00; // Send Ack
MST_Data++; // Increment Master data
P1OUT &= ~0x01; // LED off
}
else
{
USISRL = 0xFF; // Send NAck
P1OUT |= 0x01; // LED on: error
}
USICNT |= 0x01; // Bit counter = 1, send (N)Ack bit
I2C_State = 6; // Go to next state: prep for next Start
break;
}
USICTL1 &= ~USIIFG; // Clear pending flags
}
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