SPMCK16Z4MPV20 datasheet(247/500 Pages) FREESCALE

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M68HC16 Z SERIES

MULTICHANNEL COMMUNICATION INTERFACE

USER’S MANUAL

10-7

10.3.3 SPI Operating Modes

The SPI operates in either master or slave mode. Master mode is used when the MCU

originates data transfers. Slave mode is used when an external device initiates serial

transfers to the MCU. The MSTR bit in SPCR selects master or slave operation.

10.3.3.1 Master Mode

Setting the MSTR bit in SPCR selects master mode operation. In master mode, the

SPI can initiate serial transfers but cannot respond to externally initiated transfers.

When the slave-select input of a device configured for master mode is asserted, a

mode fault occurs.

When using the SPI in master mode, include the following steps:

1. Write to the MMCR, MIVR, and ILSPI. Refer to 10.5 MCCI Initialization for

more information.

2. Write to the MPAR to assign the following pins to the SPI: MISO, MOSI, and

(optionally) SS. MISO is used for serial data input in master mode, and MOSI

is used for serial data output. Either or both may be necessary, depending on

the particular application. SS is used to generate a mode fault in master mode.

If this SPI is the only possible master in the system, the SS pin may be used for

general-purpose I/O.

3. Write to the MDDR to direct the data flow on SPI pins. Configure the SCK (serial

clock) and MOSI pins as outputs. Configure MISO and (optionally) SS as in-

puts.

4. Write to the SPCR to assign values for BAUD, CPHA, CPOL, SIZE, LSBF,

WOMP, and SPIE. Set the MSTR bit to select master operation. Set the SPE

bit to enable the SPI.

5. Enable the slave device.

6. Write appropriate data to the SPI data register to initiate the transfer.

When the SPI reaches the end of the transmission, it sets the SPIF flag in the SPSR.

If the SPIE bit in the SPCR is set, an interrupt request is generated when SPIF is as-

serted. After the SPSR is read with SPIF set, and then the SPDR is read or written to,

the SPIF flag is automatically cleared.

Table 10-3 SPI Pin Functions

Pin Name

Mode

Function

Master in, slave out (MISO)

Master

Provides serial data input to the SPI

Slave

Provides serial data output from the SPI

Master out, slave in (MOSI)

Master

Provides serial output from the SPI

Slave

Provides serial input to the SPI

Serial clock (SCK)

Master

Provides clock output from the SPI

Slave

Provides clock input to the SPI

Slave select (SS)

Master

Detects bus-master mode fault

Slave

Selects the SPI for an externally-initiated serial transfer

Freescale Semiconductor, Inc.

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SPMCK16Z4MPV20 Datasheet(PDF) 247 Page - Freescale Semiconductor, Inc

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