
Serial Peripheral Interface (SPI)
SPI Registers
M68HC11E Family — Rev. 5
Data Sheet
MOTOROLA
Serial Peripheral Interface (SPI)
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139
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 
8.4 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 
8.4 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
. 
8.7.2  Serial Peripheral Status Register
SPIF — SPI Interrupt Complete Flag 
SPIF is set upon completion of data transfer between the processor and the 
external device. If SPIF goes high, and if SPIE is set, a serial peripheral interrupt 
is generated. To clear the SPIF bit, read the SPSR with SPIF set, then access 
the SPDR. Unless SPSR is read (with SPIF set) first, attempts to write SPDR 
are inhibited. 
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 
Address:
$1029
Bit 7
6
5
4
3
2
1
Bit 0
Read:
SPIF
WCOL
MODF
Write:
Reset:
0
0
0
0
0
0
0
0
= Unimplemented
Figure 8-4. Serial Peripheral Status Register (SPSR)
F
Freescale Semiconductor, Inc.
n
.