Interfacing the M68HC05 MCU to the MC145051 A/D Converter

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Freescale Semiconductor, Inc.Application NoteThe MC145051 is capable of various bit stream formats. The timingdiagram used in this application note is shown in Figure 5. TheMC145051 will wait patiently until its CS pin is asserted low. Thissignifies that a serial clock will be driving the SCLK pin to transfer thenext A/D channel address to be converted. At the same time, theMC145051 will be driving out the converted value of the previousconversion. After the 10-bit address is driven out of D OUT , the CS pin willbe driven high to signify the end of the transmission process.nc...Freescale Semiconductor, ICS16SCLK1 2 3 4 5 6 7 8 9 10 11DOUTD9 D8 D7 D6 D5 D4 D3 D2 D1 D0 LEVELDINA3 A2 A1 A0LOW H IGH ZFigure 5. MC145051 Timing DiagramAN1228 — Rev. 2.08 MOTOROLAFor More Information On This Product,Go to: www.freescale.com
Freescale Semiconductor, Inc.Application NoteDescription of the MC68HC705C8 InterfaceDescription of the MC68HC705C8 InterfaceThe following paragraphs describe the MC68HC705C8 interface.nc...Freescale Semiconductor, IHardwareThe MC68HC705C8 is one of the most popular members of theM68HC05 Family of 8-bit MCUs. It has the serial peripheral interface(SPI) that will be used to interface to the MC145051. The SPI is, inessence, an 8-bit serial shift register that can be manipulated bysoftware instructions. The SPI can be programmed with different clockpolarities and clock phases to correctly communicate with a number ofdevices. The SPI can also be configured to act as a master or a slave.Each signal of the SPI is explained below. For more detail on the SPI,consult MC68HC705C8 Technical Data, Rev. 1 (MC68HC705C8/D).SCKSerial Data ClockThe SCK signal is used to synchronize the movement of data inand out of the SPI module. This pin is an output or an inputdependent on whether the SPI is configured as a master or aslave. Data is shifted on one side of the clock edge and sampledon the other. The SCK signal can be configured to accommodatedifferent serial peripheral bus structures.MOSI Master Output, Slave InputWhen the SPI is configured as a master, this pin is used as anoutput to shift the 8-bit serial data out with the most significant bit(MSB) first. The pin is used as a slave data input when the SPI isconfigured as a slave.MISO Master Input, Slave OutputIf the SPI is configured as a master, this pin is utilized as an input.When the SPI is in slave mode, the pin is used as an output.SSSlave SelectWhen the SPI is a slave, this pin enables the SPI for an incomingtransfer. As a master, this pin should be tied high.To correctly interface to the MC145051, the SPI is configured as amaster with the timing diagram shown in Figure 6. This configurationAN1228 — Rev. 2.0MOTOROLA 9For More Information On This Product,Go to: www.freescale.com
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Interfacing the M68HC05 MCU to the MC145051 A/D Converter

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