
M68HC11E Family — Rev. 5
Data Sheet
MOTOROLA
Serial Peripheral Interface (SPI)
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Data Sheet — M68HC11E Family
Section 8. Serial Peripheral Interface (SPI)
8.1  Introduction
The serial peripheral interface (SPI), an independent serial communications 
subsystem, allows the MCU to communicate synchronously with peripheral 
devices, such as:
Frequency synthesizers
Liquid crystal display (LCD) drivers
Analog-to-digital (A/D) converter subsystems
Other microprocessors
The SPI is also capable of inter-processor communication in a multiple master 
system. The SPI system can be configured as either a master or a slave device. 
When configured as a master, data transfer rates can be as high as one-half the 
E-clock rate (1.5 Mbits per second for a 3-MHz bus frequency). When configured 
as a slave, data transfers can be as fast as the E-clock rate (3 Mbits per second for 
a 3-MHz bus frequency). 
8.2  Functional Description 
The central element in the SPI system is the block containing the shift register and 
the read data buffer. The system is single buffered in the transmit direction and 
double buffered in the receive direction. This means that new data for transmission 
cannot be written to the shifter until the previous transfer is complete; however, 
received data is transferred into a parallel read data buffer so the shifter is free to 
accept a second serial character. As long as the first character is read out of the 
read data buffer before the next serial character is ready to be transferred, no 
overrun condition occurs. A single MCU register address is used for reading data 
from the read data buffer and for writing data to the shifter. 
The SPI status block represents the SPI status functions (transfer complete, write 
collision, and mode fault) performed by the serial peripheral status register (SPSR). 
The SPI control block represents those functions that control the SPI system 
through the serial peripheral control register (SPCR). 
Refer to 
Figure 8-1
, which shows the SPI block diagram. 
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Freescale Semiconductor, Inc.
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