MC68HC908AZ32ACFU MOTOROLA [Motorola, Inc], MC68HC908AZ32ACFU Datasheet - Page 270

• Manufacturer Part Number: MC68HC908AZ32ACFU
• Description: Microcontrollers
• Manufacturer: MOTOROLA [Motorola, Inc]

Serial Peripheral Interface (SPI)
Advance Information
270
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
and Control Register
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 a transmission already has begun.
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 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 data register. (See
5).
MASTER SS
MISO/MOSI
SLAVE SS
SLAVE SS
CPHA = 0
CPHA = 1
Freescale Semiconductor, Inc.
For More Information On This Product,
Serial Peripheral Interface (SPI)
Go to: www.freescale.com
Figure 17-10. CPHA/SS Timing
BYTE 1
on page 274).
Mode Fault Error
BYTE 2
on page 261). For the state
68HC908AZ32A — Rev 0.0
BYTE 3
SPI Status
MOTOROLA
Table 17-