MC68HC705JJ7 Datasheet, PDF (96/164 Pages) Freescale Semiconductor, Inc – Microcontrollers

Simple Synchronous Serial Interface
The SIOP subsystem shares its input/output pins with port B. When the SIOP is enabled (SPE bit set in
the SCR), the port B data direction and data registers are bypassed by the SIOP. The port B data direction
and data registers will remain accessible and can be altered by the application software, but these actions
will not affect the SIOP transmitted or received data.
9.2 SIOP Signal Format
The SIOP subsystem can be software configured for master or slave operation. No external mode
selection inputs are available (for instance, no slave select pin).
9.2.1 Serial Clock (SCK)
The state of the SCK output remains a fixed logic level during idle periods between data transfers. The
edges of SCK indicate the beginning of each output data transfer and latch any incoming data received.
The first bit of transmitted data is output from the SDO pin on the first falling edge of SCK. The first bit of
received data is accepted at the SDI pin on the first rising edge of SCK after the first falling edge. The
transfer is terminated upon the eighth rising edge of SCK.
The idle state of the SCK is determined by the state of the CPHA bit in the SCR. When the CPHA is clear,
SCK will remain idle at a logic 1 as shown in Figure 9-2. When the CPHA is set, SCK will remain idle at
a logic 0 as shown in Figure 9-3. In both cases, the SDO changes data on the falling edge of the SCK,
and the SDI latches data in on the rising edge of SCK.
BIT 1 BIT 2 BIT 3 BIT 4 BIT 5 BIT 6 BIT 7 BIT 8
SDO
SCK
(CPHA = 0)
SDI
SDO
100 ns
100 ns
(IDLE = 1)
BIT 1 BIT 2 BIT 3 BIT 4 BIT 5 BIT 6 BIT 7 BIT 8
Figure 9-2. SIOP Timing Diagram (CPHA = 0)
BIT 1 BIT 2 BIT 3 BIT 4 BIT 5 BIT 6 BIT 7 BIT 8
SCK (IDLE = 0)
(CPHA = 1)
100 ns
100 ns
SDI
BIT 1 BIT 2 BIT 3 BIT 4 BIT 5 BIT 6 BIT 7 BIT 8
Figure 9-3. SIOP Timing Diagram (CPHA = 1)
The only difference in the master and slave modes of operation is the sourcing of the SCK. In master
mode, SCK is driven from an internal source within the MCU. In slave mode, SCK is driven from a source
external to the MCU. The SCK frequency is based on one of four divisions of the oscillator clock that is
selected by the SPR0 and SPR1 bits in the SCR.
MC68HC705JJ7 • MC68HC705JP7 Advance Information Data Sheet, Rev. 4.1
96
Freescale Semiconductor