s908qc16vdse Freescale Semiconductor, Inc, s908qc16vdse Datasheet - Page 184

• Manufacturer Part Number: s908qc16vdse
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Serial Peripheral Interface (SPI) Module
When an SPI is configured as a master, the SS input can be used in conjunction with the MODF flag to
prevent multiple masters from driving MOSI and SPSCK. (See
of the SS pin to set the MODF flag, the MODFEN bit in the SPSCK register must be set. If the MODFEN
bit is 0 for an SPI master, the SS pin can be used as a general-purpose I/O under the control of the data
direction register of the shared I/O port. When MODFEN is 1, it is an input-only pin to the SPI regardless
of the state of the data direction register of the shared I/O port.
User software can read the state of the SS pin by configuring the appropriate pin as an input and reading
the port data register. See
15.8 Registers
The following registers allow the user to control and monitor SPI operation:
15.8.1 SPI Control Register
The SPI control register:
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SPI control register (SPCR)
SPI status and control register (SPSCR)
SPI data register (SPDR)
Enables SPI module interrupt requests
Configures the SPI module as master or slave
Selects serial clock polarity and phase
Configures the SPSCK, MOSI, and MISO pins as open-drain outputs
Enables the SPI module
SPE
1. X = Don’t care
0
1
1
1
A high on the SS pin of a slave SPI puts the MISO pin in a high-impedance
state. The slave SPI ignores all incoming SPSCK clocks, even if it was
already in the middle of a transmission.
MASTER SS
MISO/MOSI
SPMSTR
SLAVE SS
SLAVE SS
CPHA = 0
CPHA = 1
X
0
1
1
(1)
MC68HC908QC16 • MC68HC908QC8 • MC68HC908QC4 Data Sheet, Rev. 4
MODFEN
Table 15-2.
X
X
0
1
BYTE 1
Figure 15-12. CPHA/SS Timing
Table 15-2. SPI Configuration
Master without MODF
SPI Configuration
Master with MODF
Not enabled
Slave
NOTE
BYTE 2
General-purpose I/O; SS ignored by SPI
General-purpose I/O; SS ignored by SPI
15.3.6.2 Mode Fault
Function of SS Pin
Input-only to SPI
Input-only to SPI
BYTE 3
Freescale Semiconductor
Error.) For the state