Serial Peripheral Interface (SPI)
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MC68360 USER’S MANUAL
MOTOROLA
Multi-Master Environment Support
Continuous Transfer Mode for auto scanning of a peripheral
Supports Clock Rates up to 6.25 MHz in Master Mode and up to 12.5 MHz in Slave
Mode (assuming a 25-MHz system clock)
Independent Programmable Baud Rate Generator
Programmable Clock Phase and Polarity
Open-Drain Output Pins support multi-master configuration
Local Loopback Capability for Testing
7.12.3 SPI Clocking and Pin Functions
The SPI can be configured as a master for the serial channel, meaning that it generates both
the enable and clock signals, or as slave, meaning that the enable and clock signals are
inputs to the SPI. The SPI also supports operation in a multi-master environment.
When the SPI is a master, the SPI baud rate generator is used to generate the SPI transmit
and receive clocks. The SPI baud rate generator takes its input from the BRGCLK.
The BRGCLK is generated in the clock synthesizer of the QUICC specifically for the SPI
baud rate generator and the other four baud rate generators in the CPM. BRGCLK defaults
to the system frequency (25 MHz). However, the clock synthesizer in the SIM60 has an
option to divide the BRGCLK by 1, 4, 16, or 64 before it leaves the clock synthesizer. What-
ever the resulting frequency of BRGCLK, the user may use that BRGCLK frequency as the
input to the SPI baud rate generator.
NOTE
User should note the maximum clock rate dose not equal maxi-
mum data rate. See Appendix A Serial Performance for more
detail.
The ability to reduce the frequency of BRGCLK before it leaves the clock synthesizer is use-
ful for two reasons. First, in a low-power mode, the baud rate generator clocking could be a
significant factor in overall QUICC power consumption. Thus, if none of the QUICC baud
rate generators need to generate high frequencies nor require a high resolution in the user
application, a lower frequency BRGCLK may be input to the baud rate generators. Secondly,
the user may wish to dynamically change the general system clock frequency in the clock
synthesizer (SLOW GO mode), while still having the baud rate generator run at the original
frequency. The BRGCLK allows this option also.
The SPI master-in slave-out (SPIMISO) pin is an input in master mode and an output in
slave mode. The SPI master-out slave-in (SPIMOSI) pin is an output in master mode and
an input in slave mode. The reason the pins names SPIMOSI and SPIMISO change func-
tionality between master and slave mode is to support a multi-master configuration that
allows communication from any SPI to any other SPI with the same hardware configuration.