MC68HC912BL16 Datasheet, PDF (94/128 Pages) Freescale Semiconductor, Inc – 16-Bit Microcontroller

Freescale Semiconductor, Inc.
R7/T7–R0/T0 — Receive/Transmit Data Bits 7 to 0
Reads access the eight bits of the read-only SCI receive data register (RDR). Writes access the eight
bits of the write-only SCI transmit data register (TDR). SC0DRL:SC0DRH form the 9-bit data word for
the SCI. If the SCI is being used with a 7- or 8-bit data word, only SC0DRL needs to be accessed. If a
9-bit format is used, the upper register should be written first to ensure that it is transferred to the trans-
mitter shift register with the lower register.
13.3 Serial Peripheral Interface (SPI)
The serial peripheral interface allows the MC68HC912BL16 to communicate synchronously with pe-
ripheral devices and other microprocessors. The SPI system in the MC68HC912BL16 can operate as
a master or as a slave. The SPI is also capable of interprocessor communications in a multiple master
system.
When the SPI is enabled, all pins that are defined by the configuration as inputs will be inputs regardless
of the state of the DDRS bits for those pins. All pins that are defined as SPI outputs will be outputs only
if the DDRS bits for those pins are set. Any SPI output whose corresponding DDRS bit is cleared can
be used as a general-purpose input.
A bidirectional serial pin is possible using the DDRS as the direction control.
13.3.1 SPI Baud Rate Generation
The P clock is input to a divider series and the resulting SPI clock rate may be selected to be P divided
by 2, 4, 8, 16, 32, 64, 128 or 256. Three bits in the SP0BR register control the SPI clock rate. This baud
rate generator is activated only when SPI is in the master mode and serial transfer is taking place. Oth-
erwise this divider is disabled to save power.
13.3.2 SPI Operation
In the SPI system the 8-bit data register in the master and the 8-bit data register in the slave are linked
to form a distributed 16-bit register. When a data transfer operation is performed, this 16-bit register is
serially shifted eight bit positions by the SCK clock from the master so the data is effectively exchanged
between the master and the slave. Data written to the SP0DR register of the master becomes the output
data for the slave and data read from the SP0DR register of the master after a transfer operation is the
input data from the slave.
MC68HC912BL16
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