MC908GR32AVFAE Datasheet, PDF (211/314 Pages) Freescale Semiconductor, Inc – Microcontrollers

BYTE 1
1
BYTE 2
4
BYTE 3
6
BYTE 4
8
Error Conditions
SPRF
OVRF
READ
2
5
SPSCR
READ
SPDR
3
7
1 BYTE 1 SETS SPRF BIT.
2 CPU READS SPSCR WITH SPRF BIT SET
AND OVRF BIT CLEAR.
3 CPU READS BYTE 1 IN SPDR,
CLEARING SPRF BIT.
4 BYTE 2 SETS SPRF BIT.
5 CPU READS SPSCR WITH SPRF BIT SET
AND OVRF BIT CLEAR.
6 BYTE 3 SETS OVRF BIT. BYTE 3 IS LOST.
7 CPU READS BYTE 2 IN SPDR, CLEARING SPRF BIT,
BUT NOT OVRF BIT.
8 BYTE 4 FAILS TO SET SPRF BIT BECAUSE
OVRF BIT IS NOT CLEARED. BYTE 4 IS LOST.
Figure 15-10. Missed Read of Overflow Condition
BYTE 1
SPI RECEIVE
1
COMPLETE
SPRF
BYTE 2
5
BYTE 3
7
BYTE 4
11
OVRF
READ
SPSCR
READ
SPDR
2
4
3
6
9
12
14
8
10
13
1 BYTE 1 SETS SPRF BIT.
2 CPU READS SPSCR WITH SPRF BIT SET
AND OVRF BIT CLEAR.
3 CPU READS BYTE 1 IN SPDR,
CLEARING SPRF BIT.
4 CPU READS SPSCR AGAIN
TO CHECK OVRF BIT.
5 BYTE 2 SETS SPRF BIT.
6 CPU READS SPSCR WITH SPRF BIT SET
AND OVRF BIT CLEAR.
7 BYTE 3 SETS OVRF BIT. BYTE 3 IS LOST.
8 CPU READS BYTE 2 IN SPDR,
CLEARING SPRF BIT.
9 CPU READS SPSCR AGAIN
TO CHECK OVRF BIT.
10 CPU READS BYTE 2 SPDR,
CLEARING OVRF BIT.
11 BYTE 4 SETS SPRF BIT.
12 CPU READS SPSCR.
13 CPU READS BYTE 4 IN SPDR,
CLEARING SPRF BIT.
14 CPU READS SPSCR AGAIN
TO CHECK OVRF BIT.
Figure 15-11. Clearing SPRF When OVRF Interrupt Is Not Enabled
MC68HC908GR60A • MC68HC908GR48A • MC68HC908GR32A Data Sheet, Rev. 5
Freescale Semiconductor
211