mc68hc708mp16 Freescale Semiconductor, Inc, mc68hc708mp16 Datasheet - Page 266

• Manufacturer Part Number: mc68hc708mp16
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Serial Peripheral Interface Module (SPI)
Technical Data
266
In this case, an overflow can easily be missed. Since no more SPRF
interrupts can be generated until this OVRF is serviced, it is not obvious
that bytes are being lost as more transmissions are completed. To
prevent this, either enable the OVRF interrupt or do another read of the
SPSCR following the read of the SPDR. This ensures that the OVRF
was not set before the SPRF was cleared and that future transmissions
can set the SPRF bit.
avoid this second SPSCR read, enable the OVRF to the CPU by setting
the ERRIE bit.
Figure 13-10. Clearing SPRF When OVRF Interrupt Is Not Enabled
SPI RECEIVE
COMPLETE
SPSCR
OVRF
READ
READ
SPDR
SPRF
Serial Peripheral Interface Module (SPI)
1
2
3
4
5
6
7
BYTE 1
BYTE 2 SETS SPRF BIT.
CPU READS SPSCR WITH SPRF BIT SET
AND OVRF BIT CLEAR.
BYTE 3 SETS OVRF BIT. BYTE 3 IS LOST.
BYTE 1 SETS SPRF BIT.
CPU READS SPSCR WITH SPRF BIT SET
AND OVRF BIT CLEAR.
CPU READS BYTE 1 IN SPDR,
CLEARING SPRF BIT.
CPU READS SPSCR AGAIN
TO CHECK OVRF BIT.
1
2
3
Figure 13-10
4
BYTE 2
5
illustrates this process. Generally, to
BYTE 3
6
7
8
10
11
12
13
14
8
9
MC68HC708MP16
CPU READS SPSCR AGAIN
TO CHECK OVRF BIT.
CPU READS BYTE 2 SPDR,
CLEARING OVRF BIT.
BYTE 4 SETS SPRF BIT.
CPU READS SPSCR.
CPU READS BYTE 4 IN SPDR,
CLEARING SPRF BIT.
CPU READS SPSCR AGAIN
TO CHECK OVRF BIT.
CPU READS BYTE 2 IN SPDR,
CLEARING SPRF BIT.
9
Freescale Semiconductor
BYTE 4
10
11
12
13
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Rev. 3.1
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