MC68HC908AS60ACFN FREESCALE [Freescale Semiconductor, Inc], MC68HC908AS60ACFN Datasheet - Page 217

• Manufacturer Part Number: MC68HC908AS60ACFN
• Description: M68HC08 Microcontrollers
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

19.8 Queuing Transmission Data
The double-buffered transmit data register allows a data byte to be queued and transmitted. For an SPI
configured as a master, a queued data byte is transmitted immediately after the previous transmission
has completed. The SPI transmitter empty flag (SPTE in SPSCR) indicates when the transmit data buffer
is ready to accept new data. Write to the SPI data register only when the SPTE bit is high.
shows the timing associated with doing back-to-back transmissions with the SPI (SPSCK has
CPHA:CPOL = 1:0).
For a slave, the transmit data buffer allows back-to-back transmissions to occur without the slave having
to time the write of its data between the transmissions. Also, if no new data is written to the data buffer,
the last value contained in the shift register will be the next data word transmitted.
Freescale Semiconductor
SPSCK (CPHA:CPOL = 1:0)
WRITE TO SPDR
READ SPSCR
READ SPDR
MC68HC908AZ60A • MC68HC908AS60A • MC68HC908AS60E Data Sheet, Rev. 6
1
2
3
4
5
6
BYTE 2 TRANSFERS FROM TRANSMIT DATA
REGISTER TO SHIFT REGISTER, SETTING SPTE BIT.
SPTE
SPRF
CPU WRITES BYTE 1 TO SPDR, CLEARING
SPTE BIT.
BYTE 1 TRANSFERS FROM TRANSMIT DATA
REGISTER TO SHIFT REGISTER, SETTING SPTE BIT.
CPU WRITES BYTE 2 TO SPDR, QUEUEING
BYTE 2 AND CLEARING SPTE BIT.
FIRST INCOMING BYTE TRANSFERS FROM SHIFT
REGISTER TO RECEIVE DATA REGISTER, SETTING
SPRF BIT.
CPU READS SPSCR WITH SPRF BIT SET.
MOSI
1
Figure 19-10. SPRF/SPTE CPU Interrupt Timing
MSB BIT
BYTE 1
2
6
BIT
5
3
BIT
4
BIT
3
BIT
2
BIT
1
10
11 CPU READS SPSCR WITH SPRF BIT SET.
12 CPU READS SPDR, CLEARING SPRF BIT.
7
8
9
LSB MSB BIT
5
4
CPU READS SPDR, CLEARING SPRF BIT.
CPU WRITES BYTE 3 TO SPDR, QUEUEING
BYTE 3 AND CLEARING SPTE BIT.
SECOND INCOMING BYTE TRANSFERS FROM SHIFT
REGISTER TO RECEIVE DATA REGISTER, SETTING
SPRF BIT.
BYTE 3 TRANSFERS FROM TRANSMIT DATA
REGISTER TO SHIFT REGISTER, SETTING SPTE BIT.
BYTE 2
6
6
7
BIT
5
8
BIT
4
BIT
3
BIT
2
Queuing Transmission Data
BIT
1
LSB MSB BIT
10
9
BYTE 3
11
6
12
Figure 19-10
BIT
5
BIT
4
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