MMC2114 MOTOROLA [Motorola, Inc], MMC2114 Datasheet - Page 420

• Manufacturer Part Number: MMC2114
• Description: M CORE Microcontrollers
• Manufacturer: MOTOROLA [Motorola, Inc]

Serial Peripheral Interface Module (SPI)
18.8.4 SPI Baud Rate Generation
18.8.5 Slave-Select Output
Advance Information
420
NOTE:
Also, if the slave generates a late write, its state machine may not have
time to reset, causing it to incorrectly receive a byte from the master.
This error is most likely when the SCK frequency is half the slave SPI
clock frequency. At other baud rates, the SCK skew is no more than one
SPI clock, and there is more time between the synchronized SS signal
and the first SCK edge. For example, with a SCK frequency one-fourth
the slave SPI clock frequency, there are two SPI clocks between the fall
of SS and the SCK edge.
As long as another late SPIDR write does not occur, the following bytes
to and from the slave are correctly transmitted.
The baud rate generator divides the SPI clock to produce the SPI baud
clock. The SPPR[6:4] and SPR[2:0] bits in SPIBR select the SPI clock
divisor:
where:
The baud rate generator is active only when the SPI is in master mode
and transmitting. Otherwise, the divider is inactive to reduce I
The slave-select output feature automatically drives the SS pin low
during transmission to select external devices and drives it high during
idle to deselect external devices. When SS output is selected, the SS
output pin is connected to the SS input pin of the external device.
In master mode only, setting the SSOE bit in SPICR1 and the DDRSP[3]
bit in SPIDDR configures the SS pin as a slave-select output.
Setting the SSOE bit disables the mode fault feature.
Be careful when using the slave-select output feature in a multimaster
system. The mode fault feature is not available for detecting system
errors between masters.
Freescale Semiconductor, Inc.
SPPR = the value written to bits SPPR[6:4]
SPR = the value written to bits SPR[2:0]
For More Information On This Product,
SPI clock divisor = (SPPR + 1)
Serial Peripheral Interface Module (SPI)
Go to: www.freescale.com
MMC2114 • MMC2113 • MMC2112 — Rev. 1.0
2(SPR+1)
DD
MOTOROLA
current.