mc68hc908mr24 Freescale Semiconductor, Inc, mc68hc908mr24 Datasheet - Page 278

• Manufacturer Part Number: mc68hc908mr24
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Serial Peripheral Interface Module (SPI)
Advance Information
278
NOTE:
When an SPI is configured as a slave, the SS pin is always configured
as an input. It cannot be used as a general-purpose I/O regardless of the
state of the MODFEN control bit. However, the MODFEN bit can still
prevent the state of the SS from creating a MODF error. See
Status and Control
A logic 1 voltage 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.
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
SS pin to set the MODF flag, the MODFEN bit in the SPSCK register
must be set. If the MODFEN bit is low 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. With MODFEN high, it is an input-only pin
to the SPI regardless of the state of the data direction register of the
shared I/O port.
The CPU can always read the state of the SS pin by configuring the
appropriate pin as an input and reading the port data register.
See
MASTER SS
MISO/MOSI
SLAVE SS
SLAVE SS
CPHA = 0
CPHA = 1
Table
Serial Peripheral Interface Module (SPI)
13-3.
Figure 13-12. CPHA/SS Timing
BYTE 1
Register.
13.7.2 Mode Fault
BYTE 2
Error.) For the state of the
MC68HC908MR24
Freescale Semiconductor
BYTE 3
13.13.2 SPI
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Rev. 4.1