MC68HC05C9E Datasheet, PDF (63/106 Pages) Freescale Semiconductor, Inc – Microcontrollers

Functional Description
When CPHA = 0, the shift clock is the OR of SS with SCK. In this clock phase mode, SS must go high
between successive characters in an SPI message. When CPHA = 1, SS may be left low for several SPI
characters. In cases where there is only one SPI slave MCU, its SS line could be tied to V_SS as long as
CPHA = 1 clock modes are used.
10.4 Functional Description
Figure 10-2 shows a block diagram of the serial peripheral interface circuitry. When a master device
transmits data to a slave via the MOSI line, the slave device responds by sending data to the master
device via the master’s MISO line. This implies full duplex transmission with both data out and data in
synchronized with the same clock signal. Thus, the byte transmitted is replaced by the byte received and
eliminates the need for separate transmit-empty and receive-full status bits. A single status bit (SPIF) is
used to signify that the input/output (I/O) operation has been completed.
SPI SHIFT REGISTER
76543210
S
M
PD2/
MISO
M
PD3/
S MOSI
INTERNAL DATA BUS
SPDR ($000C)
INTERNAL
CLOCK
(XTAL ÷2)
SPIE
SPE
MSTR
SPIF
WCOL
MODF
DIVIDER
÷ 2 ÷ 4 ÷ 16 ÷ 32
SPI
CONTROL
SPI INTERRUPT REQUEST
SELECT
SPI CLOCK (MASTER)
SPR1 SPR0
CLOCK
LOGIC
MSTR CPHA CPOL
SPI
CLOCK
SLAVE
SPI
CLOCK
MASTER
PD5/
SS
PD4/
SCK
7
SPI CONTROL REGISTER (SPCR) SPIE
SPI STATUS REGISTER (SPSR) SPIF
SPI DATA REGISTER (SPDR) BIT 7
6
SPE
WCOL
BIT 6
5
DWOM
0
BIT 5
4
MSTR
MODF
BIT 4
3
CPOL
0
BIT 3
2
CPHA
0
BIT 2
1
SPR1
0
BIT 1
0
SPR2
0
BIT 0
$000A
$000B
$000C
Figure 10-2. Serial Peripheral Interface Block Diagram
The SPI is double buffered on read, but not on write. If a write is performed during data transfer, the
transfer occurs uninterrupted, and the write will be unsuccessful. This condition will cause the write
collision (WCOL) status bit in the SPSR to be set. After a data byte is shifted, the SPIF flag of the SPSR
is set.
MC68HC05C9E Advance Information Data Sheet, Rev. 0.1
Freescale Semiconductor
63