SC312XDP512F0MPVR datasheet(536/1348 Pages) FREESCALE

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Chapter 12 Serial Peripheral Interface (S12SPIV4)

MC9S12XDP512 Data Sheet, Rev. 2.21

536

Freescale Semiconductor

12.4.5.2

Bidirectional Mode (MOMI or SISO)

The bidirectional mode is selected when the SPC0 bit is set in SPI control register 2 (see Table 12-8). In

this mode, the SPI uses only one serial data pin for the interface with external device(s). The MSTR bit

decides which pin to use. The MOSI pin becomes the serial data I/O (MOMI) pin for the master mode, and

the MISO pin becomes serial data I/O (SISO) pin for the slave mode. The MISO pin in master mode and

MOSI pin in slave mode are not used by the SPI.

The direction of each serial I/O pin depends on the BIDIROE bit. If the pin is conﬁgured as an output,

serial data from the shift register is driven out on the pin. The same pin is also the serial input to the shift

•

The SCK is output for the master mode and input for the slave mode.

•

The SS is the input or output for the master mode, and it is always the input for the slave mode.

•

The bidirectional mode does not affect SCK and SS functions.

NOTE

In bidirectional master mode, with mode fault enabled, both data pins MISO

and MOSI can be occupied by the SPI, though MOSI is normally used for

transmissions in bidirectional mode and MISO is not used by the SPI. If a

mode fault occurs, the SPI is automatically switched to slave mode. In this

case MISO becomes occupied by the SPI and MOSI is not used. This must

be considered, if the MISO pin is used for another purpose.

Table 12-8. Normal Mode and Bidirectional Mode

When SPE = 1

Master Mode MSTR = 1

Slave Mode MSTR = 0

Normal Mode

SPC0 = 0

Bidirectional Mode

SPC0 = 1

SPI

MOSI

MISO

Serial Out

Serial In

SPI

MOSI

MISO

Serial In

Serial Out

SPI

MOMI

Serial Out

Serial In

BIDIROE

SPI

SISO

Serial In

Serial Out

BIDIROE

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