1 /*****************************************************************************
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5 * File : USI_TWI_Master.c
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6 * Compiler : AVRGCC Toolchain version 3.4.2
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7 * Revision : $Revision: 992 $
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8 * Date : $Date: 2013-11-07 $
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9 * Updated by : $Author: Atmel $
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11 * Support mail : avr@atmel.com
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13 * Supported devices : All device with USI module can be used.
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14 * The example is written for the ATmega169, ATtiny26 and ATtiny2313
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16 * AppNote : AVR310 - Using the USI module as a TWI Master
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18 * Description : This is an implementation of an TWI master using
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19 * the USI module as basis. The implementation assumes the AVR to
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20 * be the only TWI master in the system and can therefore not be
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21 * used in a multi-master system.
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22 * Usage : Initialize the USI module by calling the USI_TWI_Master_Initialise()
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23 * function. Hence messages/data are transceived on the bus using
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24 * the USI_TWI_Transceive() function. The transceive function
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25 * returns a status byte, which can be used to evaluate the
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26 * success of the transmission.
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28 ****************************************************************************/
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31 #define F_CPU 4000000UL
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33 #define F_CPU 8000000UL
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36 #include "TWI_Master.h"
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37 #include <util/delay.h>
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39 unsigned char USI_TWI_Master_Transfer( unsigned char );
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40 unsigned char USI_TWI_Master_Stop( void );
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44 unsigned char errorState; // Can reuse the TWI_state for error states due to that it will not be need if there exists an error.
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47 unsigned char addressMode : 1;
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48 unsigned char masterWriteDataMode : 1;
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49 unsigned char unused : 6;
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53 /*---------------------------------------------------------------
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54 USI TWI single master initialization function
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55 ---------------------------------------------------------------*/
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56 void USI_TWI_Master_Initialise( void )
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58 PORT_USI |= (1<<PIN_USI_SDA); // Enable pullup on SDA, to set high as released state.
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59 PORT_USI |= (1<<PIN_USI_SCL); // Enable pullup on SCL, to set high as released state.
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61 DDR_USI |= (1<<PIN_USI_SCL); // Enable SCL as output.
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62 DDR_USI |= (1<<PIN_USI_SDA); // Enable SDA as output.
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64 USIDR = 0xFF; // Preload dataregister with "released level" data.
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65 USICR = (0<<USISIE)|(0<<USIOIE)| // Disable Interrupts.
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66 (1<<USIWM1)|(0<<USIWM0)| // Set USI in Two-wire mode.
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67 (1<<USICS1)|(0<<USICS0)|(1<<USICLK)| // Software stobe as counter clock source
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69 USISR = (1<<USISIF)|(1<<USIOIF)|(1<<USIPF)|(1<<USIDC)| // Clear flags,
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70 (0x0<<USICNT0); // and reset counter.
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73 /*---------------------------------------------------------------
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74 Use this function to get hold of the error message from the last transmission
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75 ---------------------------------------------------------------*/
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76 unsigned char USI_TWI_Get_State_Info( void )
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78 return ( USI_TWI_state.errorState ); // Return error state.
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81 /*---------------------------------------------------------------
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82 USI Transmit and receive function. LSB of first byte in data
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83 indicates if a read or write cycles is performed. If set a read
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84 operation is performed.
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86 Function generates (Repeated) Start Condition, sends address and
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87 R/W, Reads/Writes Data, and verifies/sends ACK.
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89 Success or error code is returned. Error codes are defined in
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91 ---------------------------------------------------------------*/
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92 unsigned char USI_TWI_Start_Transceiver_With_Data( unsigned char *msg, unsigned char msgSize)
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94 unsigned char tempUSISR_8bit = (1<<USISIF)|(1<<USIOIF)|(1<<USIPF)|(1<<USIDC)| // Prepare register value to: Clear flags, and
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95 (0x0<<USICNT0); // set USI to shift 8 bits i.e. count 16 clock edges.
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96 unsigned char tempUSISR_1bit = (1<<USISIF)|(1<<USIOIF)|(1<<USIPF)|(1<<USIDC)| // Prepare register value to: Clear flags, and
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97 (0xE<<USICNT0); // set USI to shift 1 bit i.e. count 2 clock edges.
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99 USI_TWI_state.errorState = 0;
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100 USI_TWI_state.addressMode = TRUE;
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102 #ifdef PARAM_VERIFICATION
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103 if(msg > (unsigned char*)RAMEND) // Test if address is outside SRAM space
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105 USI_TWI_state.errorState = USI_TWI_DATA_OUT_OF_BOUND;
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108 if(msgSize <= 1) // Test if the transmission buffer is empty
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110 USI_TWI_state.errorState = USI_TWI_NO_DATA;
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115 #ifdef NOISE_TESTING // Test if any unexpected conditions have arrived prior to this execution.
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116 if( USISR & (1<<USISIF) )
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118 USI_TWI_state.errorState = USI_TWI_UE_START_CON;
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121 if( USISR & (1<<USIPF) )
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123 USI_TWI_state.errorState = USI_TWI_UE_STOP_CON;
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126 if( USISR & (1<<USIDC) )
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128 USI_TWI_state.errorState = USI_TWI_UE_DATA_COL;
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133 if ( !(*msg & (1<<TWI_READ_BIT)) ) // The LSB in the address byte determines if is a masterRead or masterWrite operation.
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135 USI_TWI_state.masterWriteDataMode = TRUE;
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138 /* Release SCL to ensure that (repeated) Start can be performed */
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139 PORT_USI |= (1<<PIN_USI_SCL); // Release SCL.
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140 while( !(PIN_USI & (1<<PIN_USI_SCL)) ); // Verify that SCL becomes high.
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141 #ifdef TWI_FAST_MODE
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142 _delay_us( T4_TWI/4 ); // Delay for T4TWI if TWI_FAST_MODE
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144 _delay_us( T2_TWI/4 ); // Delay for T2TWI if TWI_STANDARD_MODE
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147 /* Generate Start Condition */
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148 PORT_USI &= ~(1<<PIN_USI_SDA); // Force SDA LOW.
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149 _delay_us( T4_TWI/4 );
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150 PORT_USI &= ~(1<<PIN_USI_SCL); // Pull SCL LOW.
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151 PORT_USI |= (1<<PIN_USI_SDA); // Release SDA.
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153 #ifdef SIGNAL_VERIFY
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154 if( !(USISR & (1<<USISIF)) )
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156 USI_TWI_state.errorState = USI_TWI_MISSING_START_CON;
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161 /*Write address and Read/Write data */
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164 /* If masterWrite cycle (or inital address tranmission)*/
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165 if (USI_TWI_state.addressMode || USI_TWI_state.masterWriteDataMode)
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168 PORT_USI &= ~(1<<PIN_USI_SCL); // Pull SCL LOW.
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169 USIDR = *(msg++); // Setup data.
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170 USI_TWI_Master_Transfer( tempUSISR_8bit ); // Send 8 bits on bus.
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172 /* Clock and verify (N)ACK from slave */
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173 DDR_USI &= ~(1<<PIN_USI_SDA); // Enable SDA as input.
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174 if( USI_TWI_Master_Transfer( tempUSISR_1bit ) & (1<<TWI_NACK_BIT) )
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176 if ( USI_TWI_state.addressMode )
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177 USI_TWI_state.errorState = USI_TWI_NO_ACK_ON_ADDRESS;
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179 USI_TWI_state.errorState = USI_TWI_NO_ACK_ON_DATA;
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182 USI_TWI_state.addressMode = FALSE; // Only perform address transmission once.
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184 /* Else masterRead cycle*/
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187 /* Read a data byte */
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188 DDR_USI &= ~(1<<PIN_USI_SDA); // Enable SDA as input.
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189 *(msg++) = USI_TWI_Master_Transfer( tempUSISR_8bit );
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191 /* Prepare to generate ACK (or NACK in case of End Of Transmission) */
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192 if( msgSize == 1) // If transmission of last byte was performed.
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194 USIDR = 0xFF; // Load NACK to confirm End Of Transmission.
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198 USIDR = 0x00; // Load ACK. Set data register bit 7 (output for SDA) low.
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200 USI_TWI_Master_Transfer( tempUSISR_1bit ); // Generate ACK/NACK.
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202 }while( --msgSize) ; // Until all data sent/received.
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204 USI_TWI_Master_Stop(); // Send a STOP condition on the TWI bus.
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206 /* Transmission successfully completed*/
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210 /*---------------------------------------------------------------
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211 Core function for shifting data in and out from the USI.
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212 Data to be sent has to be placed into the USIDR prior to calling
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213 this function. Data read, will be return'ed from the function.
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214 ---------------------------------------------------------------*/
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215 unsigned char USI_TWI_Master_Transfer( unsigned char temp )
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217 USISR = temp; // Set USISR according to temp.
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218 // Prepare clocking.
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219 temp = (0<<USISIE)|(0<<USIOIE)| // Interrupts disabled
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220 (1<<USIWM1)|(0<<USIWM0)| // Set USI in Two-wire mode.
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221 (1<<USICS1)|(0<<USICS0)|(1<<USICLK)| // Software clock strobe as source.
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222 (1<<USITC); // Toggle Clock Port.
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225 _delay_us( T2_TWI/4 );
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226 USICR = temp; // Generate positve SCL edge.
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227 while( !(PIN_USI & (1<<PIN_USI_SCL)) );// Wait for SCL to go high.
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228 _delay_us( T4_TWI/4 );
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229 USICR = temp; // Generate negative SCL edge.
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230 }while( !(USISR & (1<<USIOIF)) ); // Check for transfer complete.
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232 _delay_us( T2_TWI/4 );
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233 temp = USIDR; // Read out data.
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234 USIDR = 0xFF; // Release SDA.
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235 DDR_USI |= (1<<PIN_USI_SDA); // Enable SDA as output.
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237 return temp; // Return the data from the USIDR
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240 /*---------------------------------------------------------------
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241 Function for generating a TWI Stop Condition. Used to release
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243 ---------------------------------------------------------------*/
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244 unsigned char USI_TWI_Master_Stop( void )
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246 PORT_USI &= ~(1<<PIN_USI_SDA); // Pull SDA low.
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247 PORT_USI |= (1<<PIN_USI_SCL); // Release SCL.
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248 while( !(PIN_USI & (1<<PIN_USI_SCL)) ); // Wait for SCL to go high.
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249 _delay_us( T4_TWI/4 );
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250 PORT_USI |= (1<<PIN_USI_SDA); // Release SDA.
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251 _delay_us( T2_TWI/4 );
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253 #ifdef SIGNAL_VERIFY
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254 if( !(USISR & (1<<USIPF)) )
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256 USI_TWI_state.errorState = USI_TWI_MISSING_STOP_CON;
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266 unsigned char I2c_WriteByte(unsigned char msg) {
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267 unsigned char tempUSISR_8bit = (1<<USISIF)|(1<<USIOIF)|(1<<USIPF)|(1<<USIDC)| // Prepare register value to: Clear flags, and
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268 (0x0<<USICNT0); // set USI to shift 8 bits i.e. count 16 clock edges.
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269 unsigned char tempUSISR_1bit = (1<<USISIF)|(1<<USIOIF)|(1<<USIPF)|(1<<USIDC)| // Prepare register value to: Clear flags, and
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270 (0xE<<USICNT0); // set USI to shift 1 bit i.e. count 2 clock edges.
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273 PORT_USI &= ~(1<<PIN_USI_SCL); // Pull SCL LOW.
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274 USIDR = msg; // Setup data.
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275 USI_TWI_Master_Transfer( tempUSISR_8bit ); // Send 8 bits on bus.
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276 /* Clock and verify (N)ACK from slave */
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277 DDR_USI &= ~(1<<PIN_USI_SDA); // Enable SDA as input.
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278 if( USI_TWI_Master_Transfer( tempUSISR_1bit ) & (1<<TWI_NACK_BIT) ){
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279 if ( USI_TWI_state.addressMode )
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280 USI_TWI_state.errorState = USI_TWI_NO_ACK_ON_ADDRESS;
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282 USI_TWI_state.errorState = USI_TWI_NO_ACK_ON_DATA;
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287 unsigned char I2c_ReadByte(unsigned char ack_mode) {
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288 unsigned char tempUSISR_8bit = (1<<USISIF)|(1<<USIOIF)|(1<<USIPF)|(1<<USIDC)| // Prepare register value to: Clear flags, and
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289 (0x0<<USICNT0); // set USI to shift 8 bits i.e. count 16 clock edges.
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290 unsigned char tempUSISR_1bit = (1<<USISIF)|(1<<USIOIF)|(1<<USIPF)|(1<<USIDC)| // Prepare register value to: Clear flags, and
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291 (0xE<<USICNT0); // set USI to shift 1 bit i.e. count 2 clock edges.
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293 /* Read a data byte */
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294 DDR_USI &= ~(1<<PIN_USI_SDA); // Enable SDA as input.
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295 unsigned char msg = USI_TWI_Master_Transfer( tempUSISR_8bit );
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297 /* Prepare to generate ACK (or NACK in case of End Of Transmission) */
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298 if( ack_mode == NO_ACK) { // If transmission of last byte was performed.
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299 USIDR = 0xFF; // Load NACK to confirm End Of Transmission.
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301 USIDR = 0x00; // Load ACK. Set data register bit 7 (output for SDA) low.
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303 USI_TWI_Master_Transfer( tempUSISR_1bit ); // Generate ACK/NACK.
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307 void I2c_StartCondition(void) {
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308 /* Release SCL to ensure that (repeated) Start can be performed */
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309 PORT_USI |= (1<<PIN_USI_SCL); // Release SCL.
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310 while( !(PIN_USI & (1<<PIN_USI_SCL)) ); // Verify that SCL becomes high.
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311 #ifdef TWI_FAST_MODE
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312 _delay_us( T4_TWI/4 ); // Delay for T4TWI if TWI_FAST_MODE
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314 _delay_us( T2_TWI/4 ); // Delay for T2TWI if TWI_STANDARD_MODE
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317 /* Generate Start Condition */
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318 PORT_USI &= ~(1<<PIN_USI_SDA); // Force SDA LOW.
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319 _delay_us( T4_TWI/4 );
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320 PORT_USI &= ~(1<<PIN_USI_SCL); // Pull SCL LOW.
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321 PORT_USI |= (1<<PIN_USI_SDA); // Release SDA.
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325 void I2c_StopCondition(void) {
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326 USI_TWI_Master_Stop();
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