Chapter 13 Serial Peripheral Interface (S08SPIV3)
MC9S08DZ128 Series Data Sheet, Rev. 1
Freescale Semiconductor
315
13.4.3
SPI Baud Rate Register (SPIxBR)
This register is used to set the prescaler and bit rate divisor for an SPI master. This register may be read or
written at any time.
Table 13-3. SPIxC2 Register Field Descriptions
Field
Description
4
MODFEN
Master Mode-Fault Function Enable — When the SPI is congured for slave mode, this bit has no meaning or
effect. (The SS pin is the slave select input.) In master mode, this bit determines how the SS pin is used (refer
0 Mode fault function disabled, master SS pin reverts to general-purpose I/O not controlled by SPI
1 Mode fault function enabled, master SS pin acts as the mode fault input or the slave select output
3
BIDIROE
Bidirectional Mode Output Enable — When bidirectional mode is enabled by SPI pin control 0 (SPC0) = 1,
BIDIROE determines whether the SPI data output driver is enabled to the single bidirectional SPI I/O pin.
Depending on whether the SPI is congured as a master or a slave, it uses either the MOSI (MOMI) or MISO
(SISO) pin, respectively, as the single SPI data I/O pin. When SPC0 = 0, BIDIROE has no meaning or effect.
0 Output driver disabled so SPI data I/O pin acts as an input
1 SPI I/O pin enabled as an output
1
SPISWAI
SPI Stop in Wait Mode
0 SPI clocks continue to operate in wait mode
1 SPI clocks stop when the MCU enters wait mode
0
SPC0
SPI Pin Control 0 — The SPC0 bit chooses single-wire bidirectional mode. If MSTR = 0 (slave mode), the SPI
uses the MISO (SISO) pin for bidirectional SPI data transfers. If MSTR = 1 (master mode), the SPI uses the
MOSI (MOMI) pin for bidirectional SPI data transfers. When SPC0 = 1, BIDIROE is used to enable or disable the
output driver for the single bidirectional SPI I/O pin.
0 SPI uses separate pins for data input and data output
1 SPI congured for single-wire bidirectional operation
76543210
R0
SPPR2
SPPR1
SPPR0
0
SPR2
SPR1
SPR0
W
Reset
00000000
= Unimplemented or Reserved
Figure 13-7. SPI Baud Rate Register (SPIxBR)
Table 13-4. SPIxBR Register Field Descriptions
Field
Description
6:4
SPPR[2:0]
SPI Baud Rate Prescale Divisor — This 3-bit eld selects one of eight divisors for the SPI baud rate prescaler
as shown in
Table 13-5. The input to this prescaler is the bus rate clock (BUSCLK). The output of this prescaler
2:0
SPR[2:0]
SPI Baud Rate Divisor — This 3-bit eld selects one of eight divisors for the SPI baud rate divider as shown in
Table 13-6. The input to this divider comes from the SPI baud rate prescaler (see
Figure 13-4). The output of this
divider is the SPI bit rate clock for master mode.