Datasheet

17.4.8.2 Bidirectional Mode (MOMI or SISO)
The bidirectional mode is selected when the SPC0 bit is set in SPI Control Register 2 (see
the following table). In this mode, the SPI uses only one serial data pin for the interface
with one or more external devices. 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.
Table 17-23. Normal Mode and Bidirectional Mode
When SPE = 1 Master Mode MSTR = 1 Slave Mode MSTR = 0
Normal Mode
SPC0 = 0
MOSI
MISO
Serial Out
SPI
Serial In
MOSI
MISO
Serial Out
SPI
Serial In
Bidirectional Mode
SPC0 = 1
Serial Out
SPI
Serial In
MOMI
BIDIROE
Serial Out
SPI
Serial In
SISO
BIDIROE
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 register.
The SPSCK is an output for the master mode and an input for the slave mode.
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 SPSCK and
SS functions.
Note
In bidirectional master mode, with the mode fault feature
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. Consider this scenario if the MISO pin is used for another
purpose.
Functional Description
MC9S08PA60 Reference Manual, Rev. 1, 9/2012
482 Freescale Semiconductor, Inc.