MC68000 MOTOROLA [Motorola, Inc], MC68000 Datasheet - Page 378

• Manufacturer Part Number: MC68000
• Manufacturer: MOTOROLA [Motorola, Inc]

MC68302 Applications
* These bits are cleared by writing a one or setting RST in the CMR.
Figure D-9 depicts the typical cycles used on a 16-bit bus when the source data size and
destination data size are not equal. In this example, the source size is byte and the destina-
tion size is word. The IDMA performs two read cycles to obtain data and then performs a
write cycle to place data into the destination location. If the CMR SAPI bit was set, then each
byte read increments the SAPR by two. Hence, the SAPR is always pointing to the leftmost
or rightmost byte of the 16-bit bus. This type of transfer duplicates the function of an M68000
MOVEP instruction.
D-28
Done Not Synchronized—DONE is asserted as an input
during the first access of an 8-bit peripheral when operat-
ing with 1 6-bit memory.
Bus Error Source—A bus error occurred during the read
portion of an IDMA cycle.
Bus Error Destination—A bus error occurred during the
write portion of an IDMA cycle.
Normal Channel Transfer Done—The BCR decremented
to zero or the external peripheral asserted DONE and no
errors occurred during any IDMA cycle.
DTACK
NOTE: If the byte count had reached zero, DONE would be asserted by the IDMA, indicating normal transfer termination.
DONE
(OUTPUT)
(OUTPUT)
CLKO
Figure D-8. Typical IDMA External Cycles Showing Block Transfer Termination
DTACK
BGACK
AS
DACK
CLKO
AS
Figure D-9. Typical IDMA Source to Word Destination IDMA Cycles
Operation
READ 1
S0
Table D-3. Channel Status Register Bits
S1
S2
READ CYCLE
MC68302 USER’S MANUAL
S3
S4
S5
S6
DONE
DNS
BED
BES
Bit
S7
READ 2
7
Reserved
6
WRITE CYCLE
5
4
3
1
WRITE
1*
2
MOTOROLA
1*
OUTPUT
I/O
1
INPUT
1*
0