MC68HC812A4 Datasheet, PDF (272/342 Pages) Motorola, Inc – 16-bit device composed of standard on-chip peripheral modules connected by an intermodule bus. Modules include

Serial Peripheral Interface (SPI)
15.6.6 Single-Wire Operation
Normally, the SPI operates as a 2-wire interface; it uses its MOSI and
MISO pins for transmitting and receiving.
In single-wire operation, a master SPI uses the MOSI pin for both
receiving and transmitting. The MOSI pin becomes a master out, master
in (MOMI) pin. The MISO pin is disconnected from the SPI and is
available as a general-purpose port S I/O pin.
A slave SPI in single-wire operation uses the MISO pin for both receiving
and transmitting. The MISO pin becomes a slave in, slave out (SISO)
pin. The MOSI pin is disconnected from the SPI and is available as a
general-purpose I/O pin.
Setting serial pin control bit 0, SPC0, configures the SPI for single-wire
operation. The direction of the single-wire pin depends on its data
direction bit.
MASTER MODE
SERIAL OUT
SPI
SERIAL IN
DDRS5
MOMI
GENERAL-
PS4 _{PURPOSE I/O}
SLAVE MODE
SERIAL IN
SPI
SERIAL OUT
DDRS4
PS5 ^GENERAL-
PURPOSE I/O
SISO
Figure 15-8. Single-Wire Operation (SPC0 = 1)
MC68HC812A4 — Rev. 3.0
272
Serial Peripheral Interface (SPI)
Advance Information
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