1 | //******************************************************************************
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2 | // MSP430F20xx Demo - I2C Slave Receiver / Slave Transmitter, multiple bytes
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3 | //
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4 | // Description: I2C Master communicates with I2C Slave using
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5 | // the USI. Master data should increment from 0x55 with each transmitted byte.
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6 | // ACLK = n/a, MCLK = SMCLK = Calibrated 1MHz
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7 | //
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8 | // ***THIS IS THE SLAVE CODE***
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9 | //
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10 | // Slave Master
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11 | // (msp430x20x3_usi_12.c)
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12 | // MSP430F20x2/3 MSP430F20x2/3
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13 | // ----------------- -----------------
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14 | // /|\| XIN|- /|\| XIN|-
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15 | // | | | | | |
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16 | // --|RST XOUT|- --|RST XOUT|-
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17 | // | | | |
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18 | // LED <-|P1.0 | | |
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19 | // | | | P1.0|-> LED
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20 | // | SDA/P1.7|------->|P1.6/SDA |
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21 | // | SCL/P1.6|<-------|P1.7/SCL |
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22 | //
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23 | // Note: internal pull-ups are used in this example for SDA & SCL
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24 | //
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25 | // R. B. Elliott / H. Grewal
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26 | // Texas Instruments Inc.
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27 | // February 2008
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28 | // Built with IAR Embedded Workbench Version: 3.42A
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29 | //******************************************************************************
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30 |
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31 | #include <msp430x20x3.h>
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32 | #define Number_of_Bytes 5 // **** How many bytes?? ****
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33 |
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34 | void Setup_USI_Slave(void);
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35 |
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36 | char MST_Data = 0; // Variable for received data
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37 | char SLV_Data = 0x55;
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38 | char SLV_Addr = 0x90; // Address is 0x48<<1 for R/W
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39 | int I2C_State, Bytecount, transmit = 0; // State variables
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40 |
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41 | void Data_RX(void);
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42 | void TX_Data(void);
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43 | void main(void)
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44 | {
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45 | WDTCTL = WDTPW + WDTHOLD; // Stop watchdog
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46 | if (CALBC1_1MHZ ==0xFF || CALDCO_1MHZ == 0xFF)
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47 | {
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48 | while(1); // If calibration constants erased
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49 | // do not load, trap CPU!!
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50 | }
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51 | BCSCTL1 = CALBC1_1MHZ; // Set DCO
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52 | DCOCTL = CALDCO_1MHZ;
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53 | Setup_USI_Slave();
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54 |
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55 | LPM0; // CPU off, await USI interrupt
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56 | _NOP();
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57 | }
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58 |
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59 | //******************************************************************************
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60 | // USI interrupt service routine
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61 | // Rx bytes from master: State 2->4->6->8
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62 | // Tx bytes to Master: State 2->4->10->12->14
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63 | //******************************************************************************
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64 | #pragma vector = USI_VECTOR
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65 | __interrupt void USI_TXRX (void)
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66 | {
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67 | if (USICTL1 & USISTTIFG) // Start entry?
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68 | {
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69 | P1OUT |= 0x01; // LED on: sequence start
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70 | I2C_State = 2; // Enter 1st state on start
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71 | }
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72 |
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73 | switch(__even_in_range(I2C_State,14))
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74 | {
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75 | case 0: // Idle, should not get here
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76 | break;
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77 |
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78 | case 2: // RX Address
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79 | USICNT = (USICNT & 0xE0) + 0x08; // Bit counter = 8, RX address
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80 | USICTL1 &= ~USISTTIFG; // Clear start flag
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81 | I2C_State = 4; // Go to next state: check address
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82 | break;
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83 |
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84 | case 4: // Process Address and send (N)Ack
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85 | if (USISRL & 0x01){ // If master read...
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86 | SLV_Addr = 0x91; // Save R/W bit
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87 | transmit = 1;}
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88 | else{transmit = 0;
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89 | SLV_Addr = 0x90;}
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90 | USICTL0 |= USIOE; // SDA = output
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91 | if (USISRL == SLV_Addr) // Address match?
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92 | {
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93 | USISRL = 0x00; // Send Ack
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94 | P1OUT &= ~0x01; // LED off
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95 | if (transmit == 0){
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96 | I2C_State = 6;} // Go to next state: RX data
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97 | if (transmit == 1){
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98 | I2C_State = 10;} // Else go to next state: TX data
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99 | }
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100 | else
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101 | {
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102 | USISRL = 0xFF; // Send NAck
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103 | P1OUT |= 0x01; // LED on: error
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104 | I2C_State = 8; // next state: prep for next Start
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105 | }
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106 | USICNT |= 0x01; // Bit counter = 1, send (N)Ack bit
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107 | break;
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108 |
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109 | case 6: // Receive data byte
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110 | Data_RX();
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111 | break;
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112 |
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113 | case 8:// Check Data & TX (N)Ack
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114 | USICTL0 |= USIOE; // SDA = output
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115 | if (Bytecount <= (Number_of_Bytes-2))
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116 | // If not last byte
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117 | {
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118 | USISRL = 0x00; // Send Ack
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119 | I2C_State = 6; // Rcv another byte
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120 | Bytecount++;
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121 | USICNT |= 0x01; // Bit counter = 1, send (N)Ack bit
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122 | }
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123 | else // Last Byte
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124 | {
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125 | USISRL = 0xFF; // Send NAck
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126 | USICTL0 &= ~USIOE; // SDA = input
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127 | SLV_Addr = 0x90; // Reset slave address
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128 | I2C_State = 0; // Reset state machine
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129 | Bytecount =0; // Reset counter for next TX/RX
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130 | }
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131 |
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132 |
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133 | break;
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134 |
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135 | case 10: // Send Data byte
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136 | TX_Data();
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137 | break;
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138 |
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139 | case 12:// Receive Data (N)Ack
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140 | USICTL0 &= ~USIOE; // SDA = input
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141 | USICNT |= 0x01; // Bit counter = 1, receive (N)Ack
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142 | I2C_State = 14; // Go to next state: check (N)Ack
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143 | break;
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144 |
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145 | case 14:// Process Data Ack/NAck
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146 | if (USISRL & 0x01) // If Nack received...
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147 | {
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148 | USICTL0 &= ~USIOE; // SDA = input
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149 | SLV_Addr = 0x90; // Reset slave address
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150 | I2C_State = 0; // Reset state machine
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151 | Bytecount = 0;
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152 | // LPM0_EXIT; // Exit active for next transfer
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153 | }
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154 | else // Ack received
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155 | {
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156 | P1OUT &= ~0x01; // LED off
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157 | TX_Data(); // TX next byte
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158 | }
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159 | break;
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160 |
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161 | }
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162 | USICTL1 &= ~USIIFG; // Clear pending flags
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163 | }
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164 |
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165 | void Data_RX(void){
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166 |
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167 | USICTL0 &= ~USIOE; // SDA = input
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168 | USICNT |= 0x08; // Bit counter = 8, RX data
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169 | I2C_State = 8; // next state: Test data and (N)Ack
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170 | }
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171 |
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172 | void TX_Data(void){
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173 | USICTL0 |= USIOE; // SDA = output
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174 | USISRL = SLV_Data++;
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175 | USICNT |= 0x08; // Bit counter = 8, TX data
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176 | I2C_State = 12; // Go to next state: receive (N)Ack
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177 | }
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178 |
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179 | void Setup_USI_Slave(void){
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180 | P1OUT = 0xC0; // P1.6 & P1.7 Pullups
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181 | P1REN |= 0xC0; // P1.6 & P1.7 Pullups
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182 | P1DIR = 0xFF; // Unused pins as outputs
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183 | P2OUT = 0;
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184 | P2DIR = 0xFF;
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185 |
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186 | USICTL0 = USIPE6+USIPE7+USISWRST; // Port & USI mode setup
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187 | USICTL1 = USII2C+USIIE+USISTTIE; // Enable I2C mode & USI interrupts
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188 | USICKCTL = USICKPL; // Setup clock polarity
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189 | USICNT |= USIIFGCC; // Disable automatic clear control
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190 | USICTL0 &= ~USISWRST; // Enable USI
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191 | USICTL1 &= ~USIIFG; // Clear pending flag
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192 |
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193 | transmit = 0;
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194 | _EINT();
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195 |
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196 | }
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