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1 63[[[LFURFRQWUROOHUV 63, CPE 621 Advanced Microcomputer Techniques Dr. Emil Jovanov 6HULDO3HULSKHUDO,QWHUIDFH3URWRFRO USART s SPI features: Control bit SYNC in UCTL is set to select synchronous mode Supports 3 pin and 4 pin SPI operation via,, and STE Select master or slave mode Separate shift registers for receive (URXBUF) and transmit (UTXBUF) Double buffering for receive and transmit Clock polarity and clock phase control Clock frequency control in master mode Character length or 8 bits MASTER URXBUF Receive Shift MSP43 USART Transmit Buffer UTXBUF Transmit Shift Px.x STE STE.. Port.x SLAVE Shift COMMON SPI MSP43 USART as Master, external device with SPI as slave MASTER Shift COMMON SPI Px.x STE Transmit Buffer UTXBUF STE.. Port.x Transmit Shift URXBUF Receive Shift MSP43 USART SLAVE MSP43 USART as Slave in 3 pin or 4 pin configuration 1

2 86$55HJLVWHUV Control and Status s USART Control Transmit Control Receive Control Modulation Control Baud Rate 1 Select Baud Rate Select Transmit Buffer 86$5&RQWURO5HJLVWHU UCTLx Unused Unused SP CHAR Listen SYNC MM SWRST Set to select 8-bit characters; otherwise, -bit Set to enable loopback Set to select SPI; otherwise, UART Set to Select Master Mode; otherwise, Slave Mode Reset to enable USART 2

3 UDQVPLW&RQWURO5HJLVWHU UTCTLx CKPH CKPL SSEL1 SSEL Unused Unused STC TXEPT Clock Phase Set to delay clock by ½ cycle Otherwise, normal Clock Polarity Set to select Inactive level high Data is shifted out on falling edge Data is shifted in and rising edge Clock Source Select Bits Master Mode : Not used 1 : Auxiliary Clock 1-11 : Submain Clock Slave Mode External Clock always selected Slave Transmit Control Set to select 3-pin SPI Otherwise 4-pin SPI Transmit Flag Empty Master Mode Set when register and buffer empty Slave Mode Not used 5HFHLYH&RQWURO5HJLVWHU URCTLx FE Undef. OE Undef. Unused Unused Undef. Undef. Overrun Error Flag Flag is set when a character is overwritten in buffer before it s read Frame error Used in 4-pin SPI to flag bus conflicts 3

4 %DXG5DWH6HOHFW&RQWURO5HJLVWHUV UBRx UBR1x Input Clock Baud rate = [UBR1,UBR]+[UMOD] E.g. To generate a baud rate of 24 assuming the input clock is the auxiliary clock ACLK with a frequency of 32 KHz. [UBR1,UBR] = integer(aclk/baud) = int(3268/24) = int( ) = 13 or UBR1 = and UBR = 13 and UMOD is ignored. Note: Value USART modulation control register [UMOD] is ignored SPI mode UMOD is required in UART mode Max Rates: ½ input clock in Master Mode 'DWD%XIIHU5HJLVWHUV URXBUFx Reading resets the receive-interrupt flag URXIFG UTXBUFx Transmitting sets the transmit transmit-interrupt flag ITXIFG 4

5 6ROLG6WDWH9RLFH5HFRUGHU Analog Digital Analog Pre-amp & Filter MSP43 ADC12 USART P3. P3.1 Serial DAC DIN CS Active Filter & Amp. Microphone A switch controls Record/Play operation Input to MSP43 is through the built-in ADC12 Input data is stored flash memory Output from MSP43 is through USART pin is not used in 3-pin SPI Switch off enables DAC playback Speaker 9RLFH5HFRUGHU6HWXS UCTL Unused Unused Unused CHAR Listen SYNC MM SWRST Select 8-bit characters Select SPI in Master Mode UTCTL CKPH CKPL SSEL1 SSEL Unused Unused STC TXEPT Shift Data out on falling edge Select SMCLK Select 3-pin SPI UBR 1 UBR1 5

6 63,%DVHG'DWD$FTXLVLWLRQ Master Slave The application describes the use of 3-pin SPI in master mode with 2 slaves When the I/O is low, MSP43 reads from ADC. The ADC reads from signal input when CS is high When I/O is high, MSP43 writes to DAC I/O pin is used to control which slave to enable. It s not part of the 3-pin SPI. It can be controlled UTXIFG or URXIFG Data I/O is as 8-bit words MSP43 I/O P4.1 P4.5 P4. DIN CS Serial DAC Slave Serial ADC Recons. Input Signal Input P4.4 CS DOUT 63,%DVHG'DWD$FTXLVLWLRQ6HWXS UCTL Unused Unused Unused CHAR Listen SYNC MM SWRST Select 8-bit characters Select SPI in Master Mode UTCTL CKPH CKPL SSEL1 SSEL Unused Unused STC TXEPT Shift Data out on falling edge Select SMCLK Select 3-pin SPI UBR 1 UBR1 6