MC68HC705 MOTOROLA [Motorola, Inc], MC68HC705 Datasheet - Page 140

• Manufacturer Part Number: MC68HC705
• Description: HCMOS Microcontroller Unit
• Manufacturer: MOTOROLA [Motorola, Inc]

Serial Peripheral Interface (SPI)
11.4 Operation
Technical Data
140
$000C
$000A
$000B
Addr.
SPI Control Register
SPI Status Register
SPI Data Register
Register Name
See page 147.
See page 149.
See page 147.
(SPCR)
(SPDR)
(SPSR)
The master/slave SPI allows full-duplex, synchronous, serial
communication between the microcontroller unit (MCU) and peripheral
devices, including other MCUs. As the 8-bit shift register of a master SPI
transmits each byte to another device, a byte from the receiving device
enters the master SPI shift register. A clock signal from the master SPI
synchronizes data transmission.
Only a master SPI can initiate transmissions. Software begins the
transmission from a master SPI by writing to the SPI data register
(SPDR). The SPDR does not buffer data being transmitted from the SPI.
Data written to the SPDR goes directly into the shift register and begins
the transmission immediately under the control of the serial clock. The
transmission ends after eight cycles of the serial clock when the SPI flag
(SPIF) becomes set. At the same time that SPIF becomes set, the data
shifted into the master SPI from the receiving device transfers to the
SPDR. The SPDR buffers data being received by the SPI. Before the
master SPI sends the next byte, software must clear the SPIF bit by
reading the SPSR and then accessing the SPDR.
Figure 11-2. SPI I/O Register Summary
Reset:
Reset:
Reset:
Read:
Read:
Read:
Write:
Write:
Write:
Serial Peripheral Interface (SPI)
SPIE
SPIF
Bit 7
Bit 7
0
0
= Unimplemented
WCOL
SPE
Bit 6
6
0
0
Bit 5
5
U = Unaffected
MODF
MSTR
Unaffected by reset
Bit 4
4
0
0
CPOL
Bit 3
U
3
MC68HC705C8A — Rev. 2.0
CPHA
BIt 2
U
2
SPR1
Bit 1
U
1
MOTOROLA
SPR0
Bit 0
Bit 0
U