MC9S08JM16 Datasheet, PDF (258/386 Pages) Freescale Semiconductor, Inc – Microcontrollers

Serial Peripheral Interface (S08SPI16V1)
The baud rate divisor equation is as follows:
BaudRateDivisor = (SPPR + 1) • 2^{(SPR + 1)}
The baud rate can be calculated with the following equation:
Baud Rate = BusClock ⁄ BaudRateDivisor
BUS CLOCK
PRESCALER
DIVIDE BY
1, 2, 3, 4, 5, 6, 7, or 8
BAUD RATE DIVIDER
DIVIDE BY
2, 4, 8, 16, 32, 64, 128, or 256
MASTER
SPI
BIT RATE
SPPR2:SPPR1:SPPR0
SPR2:SPR1:SPR0
Figure 15-15. SPI Baud Rate Generation
15.4.7 Special Features
15.4.7.1 SS Output
The SS 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.
The SS output is available only in master mode during normal SPI operation by asserting the SSOE and
MODFEN bits as shown in Table 15-2.
The mode fault feature is disabled while SS output is enabled.
NOTE
Care must be taken when using the SS output feature in a multi-master
system since the mode fault feature is not available for detecting system
errors between masters.
15.4.7.2 Bidirectional Mode (MOMI or SISO)
The bidirectional mode is selected when the SPC0 bit is set in SPI Control Register 2 (see Table 15-9.) In
this mode, the SPI uses only one serial data pin for the interface with external device(s). The MSTR bit
decides which pin to use. The MOSI pin becomes the serial data I/O (MOMI) pin for the master mode, and
the MISO pin becomes serial data I/O (SISO) pin for the slave mode. The MISO pin in master mode and
MOSI pin in slave mode are not used by the SPI.
MC9S08JM16 Series Data Sheet, Rev. 2
258
Freescale Semiconductor