MC68HC812A4 Datasheet, PDF (280/342 Pages) Motorola, Inc – 16-bit device composed of standard on-chip peripheral modules connected by an intermodule bus. Modules include

Serial Peripheral Interface (SPI)
15.8.4 SS (Slave Select)
The SS pin has multiple functions that depend on SPI configuration:
• The SS pin of a slave SPI is always configured as an input and
allows the slave to be selected for transmission.
• When the CPHA bit is clear, the SS pin signals the start of a
transmission.
• The SS pin of a master SPI can be configured as a mode-fault
input, a slave-select output, or a general-purpose output.
– As a mode-fault input (MSTR = 1, DDRS7 = 0, SSOE = 0), the
SS pin can detect multiple masters driving MOSI and SPSCK.
– As a slave-select output (MSTR = 1, DDRS7 = 1, SSOE = 1),
the SS pin can select slaves for transmission.
– When MSTR = 1, DDRS7 = 1, and SSOE = 0, the SS pin is
available as a general-purpose output.
15.9 Low-Power Options
This section describes the three low-power modes:
• Run mode
• Wait mode
• Stop mode
15.9.1 Run Mode
Clearing the SPI enable bit, SPE, in SPI control register 1 reduces power
consumption in run mode. SPI registers are still accessible when SPE is
cleared, but clocks to the core of the SPI are disabled.
15.9.2 Wait Mode
The SPI remains active in wait mode. Any enabled interrupt request from
the SPI can bring the MCU out of wait mode.
MC68HC812A4 — Rev. 3.0
280
Serial Peripheral Interface (SPI)
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