分析以下贴出的代码，为什么在receiveCount为1的时候调用了USCI_B_I2C_masterReceiveMultiByteFinish，而获取最后一个字节的时候，调用了USCI_B_I2C_masterReceiveMultiByteNext？ /* --COPYRIGHT--,BSD * Copyright (c) 2017, Texas Instruments Incorporated * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * * Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * * Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * * Neither the name of Texas Instruments Incorporated nor the names of * its contributors may be used to endorse or promote products derived * from this software without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. * --/COPYRIGHT--*/ #include "driverlib.h" //***************************************************************************** //! This example shows how to configure the I2C module as a master for //! multi-byte reception with help of interrupts. The address of the slave module //! that the master communicating with also set in this example. This example uses //! the interrupt driven mode to receive data. //! //! This example uses the following peripherals and I/O signals. You must //! review these and change as needed for your own board: //! - I2C peripheral //! - GPIO Port peripheral (for I2C pins) //! - SCL2 //! - SDA //! //! This example uses the following interrupt handlers. To use this example //! in your own application you must add these interrupt handlers to your //! vector table. //! - USCI_B0_VECTOR //! // //***************************************************************************** //***************************************************************************** // //Set the address for slave module. This is a 7-bit address sent in the //following format: //[A6:A5:A4:A3:A2:A1:A0:RS] // //A zero in the "RS" position of the first byte means that the master //transmits (sends) data to the selected slave, and a one in this position //means that the master receives data from the slave. // //***************************************************************************** #define SLAVE_ADDRESS 0x48 //***************************************************************************** // //Specify Expected Receive data count. // //***************************************************************************** #define RXCOUNT 0x05 unsigned char receiveBuffer[10] = { 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01}; unsigned char *receiveBufferPointer; unsigned char receiveCount = 0; void main () { //Stop WDT WDT_A_hold(WDT_A_BASE); //Assign I2C pins to USCI_B0 GPIO_setAsPeripheralModuleFunctionInputPin( GPIO_PORT_P3, GPIO_PIN1 + GPIO_PIN2 ); //Initialize Master USCI_B_I2C_initMasterParam param = {0}; param.selectClockSource = USCI_B_I2C_CLOCKSOURCE_SMCLK; param.i2cClk = UCS_getSMCLK(); param.dataRate = USCI_B_I2C_SET_DATA_RATE_100KBPS; USCI_B_I2C_initMaster(USCI_B0_BASE, &param); //Specify slave address USCI_B_I2C_setSlaveAddress(USCI_B0_BASE, SLAVE_ADDRESS ); //Set receive mode USCI_B_I2C_setMode(USCI_B0_BASE, USCI_B_I2C_RECEIVE_MODE ); //Enable I2C Module to start operations USCI_B_I2C_enable(USCI_B0_BASE); //Enable master Receive interrupt USCI_B_I2C_enableInterrupt(USCI_B0_BASE, USCI_B_I2C_RECEIVE_INTERRUPT ); //wait for bus to be free while (USCI_B_I2C_isBusBusy(USCI_B0_BASE )) ; while (1) { receiveBufferPointer = (unsigned char *)receiveBuffer; receiveCount = RXCOUNT; //Initialize multi reception USCI_B_I2C_masterReceiveMultiByteStart(USCI_B0_BASE); //Enter low power mode 0 with interrupts enabled. __bis_SR_register(LPM0_bits + GIE); __no_operation(); } } //****************************************************************************** // //This is the USCI_B0 interrupt vector service routine. // //****************************************************************************** #if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__) #pragma vector=USCI_B0_VECTOR __interrupt #elif defined(__GNUC__) __attribute__((interrupt(USCI_B0_VECTOR))) #endif void USCI_B0_ISR (void) { switch (__even_in_range(UCB0IV,12)){ case USCI_I2C_UCRXIFG: { //Decrement RX byte counter receiveCount--; if (receiveCount){ if (receiveCount == 1) { //Initiate end of reception -> Receive byte with NAK *receiveBufferPointer++ = USCI_B_I2C_masterReceiveMultiByteFinish( USCI_B0_BASE ); } else { //Keep receiving one byte at a time *receiveBufferPointer++ = USCI_B_I2C_masterReceiveMultiByteNext( USCI_B0_BASE ); } } else { //Receive last byte *receiveBufferPointer = USCI_B_I2C_masterReceiveMultiByteNext( USCI_B0_BASE ); __bic_SR_register_on_exit(LPM0_bits); } break; } } }