mc68hc705c9a Freescale Semiconductor, Inc, mc68hc705c9a Datasheet - Page 72

• Manufacturer Part Number: mc68hc705c9a
• Description: M68hc05 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Serial Peripheral Interface (SPI)
10.3.1 Master In Slave Out (MISO)
The MISO line is configured as an input in a master device and as an output in a slave device. It is one
of the two lines that transfer serial data in one direction, with the most significant bit sent first. The MISO
line of a slave device is placed in the high-impedance state if the slave is not selected.
10.3.2 Master Out Slave In (MOSI)
The MOSI line is configured as an output in a master device and as an input in a slave device. It is one
of the two lines that transfer serial data in one direction with the most significant bit sent first.
10.3.3 Serial Clock (SCK)
The master clock is used to synchronize data movement both in and out of the device through its MOSI
and MISO lines. The master and slave devices are capable of exchanging a byte of information during a
sequence of eight clock cycles. Since SCK is generated by the master device, this line becomes an input
on a slave device.
As shown in
and CPHA in the serial peripheral control register (SPCR). Both master and slave devices must operate
with the same timing. The master device always places data on the MOSI line a half cycle before the clock
edge (SCK), in order for the slave device to latch the data.
Two bits (SPR0 and SPR1) in the SPCR of the master device select the clock rate. In a slave device,
SPR0 and SPR1 have no effect on the operation of the SPI.
10.3.4 Slave Select (SS)
The slave select (SS) input line is used to select a slave device. It has to be low prior to data transactions
and must stay low for the duration of the transaction.The SS line on the master must be tied high. In
master mode, if the SS pin is pulled low during a transmission, a mode fault error flag (MODF) is set in
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Figure
MISO/MOSI
SCK
SCK
SCK
SCK
SS
10-1, four possible timing relationships may be chosen by using control bits CPOL
MC68HC05C9A Advance Information Data Sheet, Rev. 4.1
MSB
Figure 10-1. Data Clock Timing Diagram
6
INTERNAL STROBE FOR DATA CAPTURE (ALL MODES)
5
4
3
2
1
0
Freescale Semiconductor
CPOL = 0
CPHA = 0
CPOL = 0
CPHA = 1
CPOL = 1
CPHA = 0
CPOL = 1
CPHA = 1