MC908AP32CFBE Freescale, MC908AP32CFBE Datasheet - Page 225

• Manufacturer Part Number: MC908AP32CFBE
• Manufacturer: Freescale

Specifications of MC908AP32CFBE

• Cpu Family: HC08
• Device Core Size: 8b
• Frequency (max): 8MHz
• Interface Type: SCI/SPI
• Total Internal Ram Size: 2KB
• # I/os (max): 32
• Number Of Timers - General Purpose: 4
• Operating Supply Voltage (typ): 3.3/5V
• Operating Supply Voltage (max): 5.5V
• Operating Supply Voltage (min): 2.7V
• On-chip Adc: 8-chx10-bit
• Instruction Set Architecture: CISC
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 44
• Package Type: PQFP
• Program Memory Type: Flash
• Program Memory Size: 32KB
• Lead Free Status / RoHS Status: Compliant

13.12.4 SS (Slave Select)
The SS pin has various functions depending on the current state of the SPI. For an SPI configured as a
slave, the SS is used to select a slave. For CPHA = 0, the SS is used to define the start of a transmission.
(See
toggled high and low between each byte transmitted for the CPHA = 0 format. However, it can remain low
between transmissions for the CPHA = 1 format. See
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
Register.)
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
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 port data register. (See
Freescale Semiconductor
13.5 Transmission
MASTER SS
SPE
MISO/MOSI
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.
Note 1. X = Don’t care
0
1
1
1
SLAVE SS
SLAVE SS
CPHA = 0
CPHA = 1
SPMSTR
Formats.) Since it is used to indicate the start of a transmission, the SS must be
X
0
1
1
(1)
MODFEN
MC68HC908AP Family Data Sheet, Rev. 4
Figure 13-12. CPHA/SS Timing
BYTE 1
Table
Table 13-3. SPI Configuration
X
X
0
1
13-3.)
Master without MODF
SPI Configuration
Master with MODF
NOTE
Not enabled
Slave
Figure
BYTE 2
13-12.
13.7.2 Mode Fault
13.13.2 SPI Status and Control
General-purpose I/O;
General-purpose I/O;
State of SS Logic
SS ignored by SPI
SS ignored by SPI
Input-only to SPI
Input-only to SPI
BYTE 3
Error.) For the state of
I/O Signals
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