Technical Data
MC68HC11E Family
—
Rev. 4
174
Serial Peripheral Interface (SPI)
MOTOROLA
Serial Peripheral Interface (SPI)
CPOL
—
Clock Polarity Bit
When the clock polarity bit is cleared and data is not being
transferred, the SCK pin of the master device has a steady state low
value. When CPOL is set, SCK idles high. Refer to
Figure 8-2
and
8.5 Clock Phase and Polarity Controls
.
CPHA
—
Clock Phase Bit
The clock phase bit, in conjunction with the CPOL bit, controls the
clock-data relationship between master and slave. The CPHA bit
selects one of two different clocking protocols. Refer to
Figure 8-2
and
8.5 Clock Phase and Polarity Controls
.
SPR[1:0]
—
SPI Clock Rate Select Bits
These two bits select the SPI clock (SCK) rate when the device is
configured as master. When the device is configured as slave, these
bits have no effect. Refer to
Table 8-1
.
Table 8-1. SPI Clock Rates
SPR[1:0]
Divide
E Clock By
Frequency at
E = 1 MHz (Baud)
Frequency at
E = 2 MHz (Baud)
Frequency at
E = 3 MHz (Baud)
Frequency at
E = 4 MHz (Baud)
0 0
2
500 kHz
1.0 MHz
1.5 MHz
2 MHz
0 1
4
250 kHz
500 kHz
750 kHz
1 MHz
1 0
16
62.5 kHz
125 kHz
187.5 kHz
250 kHz
1 1
32
31.3 kHz
62.5 kHz
93.8 kHz
125 kHz