mc68hc908gr16 Freescale Semiconductor, Inc, mc68hc908gr16 Datasheet - Page 202

• Manufacturer Part Number: mc68hc908gr16
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Serial Peripheral Interface (SPI) Module
signal. When CPHA = 0, the SPSCK signal remains inactive for the first half of the first SPSCK cycle.
When CPHA = 1, the first SPSCK cycle begins with an edge on the SPSCK line from its inactive to its
active level. The SPI clock rate (selected by SPR1:SPR0) affects the delay from the write to SPDR and
the start of the SPI transmission. (See
derivative of the internal MCU clock. To conserve power, it is enabled only when both the SPE and
SPMSTR bits are set. SPSCK edges occur halfway through the low time of the internal MCU clock. Since
the SPI clock is free-running, it is uncertain where the write to the SPDR occurs relative to the slower
SPSCK. This uncertainty causes the variation in the initiation delay shown in
no longer than a single SPI bit time. That is, the maximum delay is two MCU bus cycles for DIV2, eight
MCU bus cycles for DIV8, 32 MCU bus cycles for DIV32, and 128 MCU bus cycles for DIV128.
202
SPSCK CYCLE
CPHA = 1
CPHA = 0
NUMBER
CLOCK
CLOCK
CLOCK
CLOCK
CLOCK
SPSCK
SPSCK
MOSI
BUS
BUS
BUS
BUS
BUS
Figure 16-8. Transmission Start Delay (Master)
TO SPDR
TO SPDR
TO SPDR
WRITE
WRITE
WRITE
TO SPDR
TO SPDR
WRITE
WRITE
EARLIEST
EARLIEST
EARLIEST
EARLIEST
MC68HC908GR16 Data Sheet, Rev. 5.0
INITIATION DELAY FROM WRITE SPDR TO TRANSFER BEGIN
Figure
LATEST
SPSCK = INTERNAL CLOCK ÷ 128;
SPSCK = INTERNAL CLOCK ÷ 32;
16-8.) The internal SPI clock in the master is a free-running
SPSCK = INTERNAL CLOCK ÷ 8;
INITIATION DELAY
128 POSSIBLE START POINTS
32 POSSIBLE START POINTS
8 POSSIBLE START POINTS
SPSCK = INTERNAL CLOCK ÷ 2;
2 POSSIBLE START POINTS
MSB
1
BIT 6
2
LATEST
LATEST
LATEST
Figure
BIT 5
3
Freescale Semiconductor
16-8. This delay is