System Integration Block (SIB)
3-6
MC68302 USER’S MANUAL
MOTOROLA
NOTE
These percentages are valid only when using internal limited re-
quest generation (REQG = 00).
RST—Software Reset
This bit will reset the IDMA to the same state as an external reset. The IDMA clears RST
when the reset is complete.
0 = Normal operation
1 = The channel aborts any external pending or running bus cycles and terminates
channel operation. Setting RST clears all bits in the CSR and CMR.
STR—Start Operation
This bit starts the IDMA transfer if the REQG bits are programmed for an internal request.
(The IDMA begins requesting the M68000 bus one clock after STR is set.) If the REQG
bits are programmed for an external request, this bit must be set before the IDMA will rec-
ognize the first request on the DREQ input.
0 = Stop channel; clearing this bit will cause the IDMA to stop transferring data at
the end of the current operand transfer. The IDMA internal state is not altered.
1 = Start channel; setting this bit will allow the IDMA to start (or continue if previously
stopped) transferring data.
NOTE
STR is cleared automatically when the transfer is complete.
3.1.2.2 Source Address Pointer Register (SAPR)
The SAPR is a 32-bit register.
The SAPR contains 24 (A23–A0) address bits of the source operand used by the IDMA to
access memory or memory-mapped peripheral controller registers. During the IDMA read
cycle, the address on the master address bus is driven from this register. The SAPR may
be programmed by the SAPI bit to be incremented or remain constant after each operand
transfer.
The register is incremented using unsigned arithmetic and will roll over if an overflow occurs.
For example, if a register contains $00FFFFFF and is incremented by one, it will roll over to
$00000000. This register can be incremented by one or two, depending on the SSIZE bit
and the starting address in this register.
3.1.2.3 Destination Address Pointer Register (DAPR)
The DAPR is a 32-bit register.
31
24
23
0
RESERVED
SOURCE ADDRESS POINTER
31
24
23
0
RESERVED
DESTINATION ADDRESS POINTER