Serial Peripheral Interface (SPI) Module
I/O Signals
MC68HC08GP32A MC68HC08GP16A
Data Sheet
MOTOROLA
Serial Peripheral Interface (SPI) Module
211
To allow software to clear status bits during a break interrupt, write a 1 to BCFE. If
a status bit is cleared during the break state, it remains cleared when the MCU exits
the break state.
To protect status bits during the break state, write a 0 to BCFE. With BCFE at 0 (its
default state), software can read and write I/O registers during the break state
without affecting status bits. Some status bits have a 2-step read/write clearing
procedure. If software does the first step on such a bit before the break, the bit
cannot change during the break state as long as BCFE is 0. After the break, doing
the second step clears the status bit.
Since the SPTE bit cannot be cleared during a break with BCFE cleared, a write to
the transmit data register in break mode does not initiate a transmission nor is this
data transferred into the shift register. Therefore, a write to the SPDR in break
mode with BCFE cleared has no effect.
16.11 I/O Signals
The SPI module has four I/O pins:
MISO — Master input/slave output
MOSI — Master output/slave input
SPSCK — Serial clock
SS — Slave select
16.11.1 MISO (Master In/Slave Out)
MISO is one of the two SPI module pins that transmits serial data. In full duplex
operation, the MISO pin of the master SPI module is connected to the MISO pin of
the slave SPI module. The master SPI simultaneously receives data on its MISO
pin and transmits data from its MOSI pin.
Slave output data on the MISO pin is enabled only when the SPI is configured as
a slave. The SPI is configured as a slave when its SPMSTR bit is 0 and its SS pin
is low. To support a multiple-slave system, a high on the SS pin puts the MISO pin
in a high-impedance state.
When enabled, the SPI controls data direction of the MISO pin regardless of the
state of the data direction register of the shared I/O port.
16.11.2 MOSI (Master Out/Slave In)
MOSI is one of the two SPI module pins that transmits serial data. In full-duplex
operation, the MOSI pin of the master SPI module is connected to the MOSI pin of
the slave SPI module. The master SPI simultaneously transmits data from its MOSI
pin and receives data on its MISO pin.
When enabled, the SPI controls data direction of the MOSI pin regardless of the
state of the data direction register of the shared I/O port.