mcf51jf128 Freescale Semiconductor, Inc, mcf51jf128 Datasheet - Page 937

• Manufacturer Part Number: mcf51jf128
• Description: Mcf51jf128 Reference Manual
• Manufacturer: Freescale Semiconductor, Inc

38.4.9.2 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.
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.
Freescale Semiconductor, Inc.
Bidirectional Mode
When SPE = 1
Normal Mode
SPC0 = 0
SPC0 = 1
Be careful when using the SS output feature in a multimaster
system because the mode fault feature is not available for
detecting system errors between masters.
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
Table 38-34. Normal Mode and Bidirectional Mode
Serial Out
Serial Out
Serial In
Serial In
SPI
SPI
MCF51JF128 Reference Manual, Rev. 2, 03/2011
Master Mode MSTR = 1
BIDIROE
Preliminary
Note
Note
MOMI
MOSI
MISO
Chapter 38 Serial Peripheral Interface (SPI)
Serial Out
Serial Out
Serial In
Serial In
SPI
SPI
Slave Mode MSTR = 0
BIDIROE
MOSI
MISO
SISO
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