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//****************************************************************************** // MSP430G2x21/G2x31 Demo - I2C Master Transmitter / Reciever, multiple bytes // // Description: I2C Master communicates with I2C Slave using // the USI. Master data should increment from 0x55 with each transmitted byte // and Master determines the number of bytes recieved, set by // the Number_of_Bytes value. LED off for address or data Ack; // LED on for address or data NAck. // ACLK = n/a, MCLK = SMCLK = Calibrated 1MHz // // // ***THIS IS THE MASTER CODE*** // // Slave Master // (msp430g2x21_usi_15.c) // MSP430G2x21/G2x31 MSP430G2x21/G2x31 // ----------------- ----------------- // /|\| XIN|- /|\| XIN|- // | | | | | | // --|RST XOUT|- --|RST XOUT|- // | | | | // LED <-|P1.0 | | | // | | | P1.0|-> LED // | SDA/P1.7|------->|P1.6/SDA | // | SCL/P1.6|<-------|P1.7/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 //******************************************************************************
while(1) { Master_Transmit(); _NOP(); // Used for IAR
Master_Recieve(); _NOP(); } }
/****************************************************** // USI interrupt service routine // Data Transmit : state 0 -> 2 -> 4 -> 10 -> 12 -> 14 // Data Recieve : state 0 -> 2 -> 4 -> 6 -> 8 -> 14 ******************************************************/ #pragma vector = USI_VECTOR __interrupt void USI_TXRX (void) { switch(__even_in_range(I2C_State,14)) { case 0: // Generate Start Condition & send address to slave P1OUT |= 0x01; // LED on: sequence start Bytecount = 0; USISRL = 0x00; // Generate Start Condition... USICTL0 |= USIGE+USIOE; USICTL0 &= ~USIGE; if (Transmit == 1){ USISRL = 0x90; // Address is 0x48 << 1 bit + 0 (rw) } if (Transmit == 0){ USISRL = 0x91; // 0x91 Address is 0x48 << 1 bit // + 1 for Read } USICNT = (USICNT & 0xE0) + 0x08; // Bit counter = 8, TX Address I2C_State = 2; // next state: rcv address (N)Ack break;
case 2: // Receive Address Ack/Nack bit USICTL0 &= ~USIOE; // SDA = input USICNT |= 0x01; // Bit counter=1, receive (N)Ack bit I2C_State = 4; // Go to next state: check (N)Ack break;
case 4: // Process Address Ack/Nack & handle data TX
if(Transmit == 1){ USICTL0 |= USIOE; // SDA = output if (USISRL & 0x01) // If Nack received... { // Send stop... USISRL = 0x00; USICNT |= 0x01; // Bit counter=1, SCL high, SDA low I2C_State = 14; // Go to next state: generate Stop P1OUT |= 0x01; // Turn on LED: error } else { // Ack received, TX data to slave... USISRL = MST_Data++; // Load data byte USICNT |= 0x08; // Bit counter = 8, start TX I2C_State = 10; // next state: receive data (N)Ack Bytecount++; P1OUT &= ~0x01; // Turn off LED break; } } if(Transmit == 0){
if (USISRL & 0x01) // If Nack received { // Prep Stop Condition USICTL0 |= USIOE; USISRL = 0x00; USICNT |= 0x01; // Bit counter= 1, SCL high, SDA low I2C_State = 8; // Go to next state: generate Stop P1OUT |= 0x01; // Turn on LED: error } else{ Data_RX();} // Ack received
} break;
case 6: // Send Data Ack/Nack bit USICTL0 |= USIOE; // SDA = output if (Bytecount <= number_of_bytes-2) { // If this is not the last byte USISRL = 0x00; // Send Ack P1OUT &= ~0x01; // LED off I2C_State = 4; // Go to next state: data/rcv again Bytecount++; }
else //last byte: send NACK { USISRL = 0xFF; // Send NAck P1OUT |= 0x01; // LED on: end of comm I2C_State = 8; // stop condition } USICNT |= 0x01; // Bit counter = 1, send (N)Ack bit break;
case 8: // Prep Stop Condition USICTL0 |= USIOE; // SDA = output USISRL = 0x00; USICNT |= 0x01; // Bit counter= 1, SCL high, SDA low I2C_State = 14; // Go to next state: generate Stop break;
case 10: // Receive Data Ack/Nack bit USICTL0 &= ~USIOE; // SDA = input USICNT |= 0x01; // Bit counter = 1, receive (N)Ack bit I2C_State = 12; // Go to next state: check (N)Ack break;
case 12: // Process Data Ack/Nack & send Stop USICTL0 |= USIOE; if (Bytecount == number_of_bytes){// If last byte USISRL = 0x00;
I2C_State = 14; // Go to next state: generate Stop P1OUT |= 0x01; USICNT |= 0x01; } // set count=1 to trigger next state else{ P1OUT &= ~0x01; // Turn off LED Data_TX(); // TX byte } break;
case 14:// Generate Stop Condition USISRL = 0x0FF; // USISRL = 1 to release SDA USICTL0 |= USIGE; // Transparent latch enabled USICTL0 &= ~(USIGE+USIOE); // Latch/SDA output disabled I2C_State = 0; // Reset state machine for next xmt LPM0_EXIT; // Exit active for next transfer break; }
USICTL1 &= ~USIIFG; // Clear pending flag }
void Data_TX (void){
USISRL = MST_Data++; // Load data byte USICNT |= 0x08; // Bit counter = 8, start TX I2C_State = 10; // next state: receive data (N)Ack Bytecount++; }
void Data_RX (void){ USICTL0 &= ~USIOE; // SDA = input --> redundant USICNT |= 0x08; // Bit counter = 8, RX data I2C_State = 6; // Next state: Test data and (N)Ack P1OUT &= ~0x01; // LED off }
void Master_Transmit(void){ Setup_USI_Master_TX(); USICTL1 |= USIIFG; // Set flag and start communication LPM0; // CPU off, await USI interrupt __delay_cycles(10000); // Delay between comm cycles } void Master_Recieve(void){ Setup_USI_Master_RX(); USICTL1 |= USIIFG; // Set flag and start communication LPM0; // CPU off, await USI interrupt __delay_cycles(10000); // Delay between comm cycles }
