Intel386™ EX EMBEDDED MICROPROCESSOR USER’S MANUAL
12-42
12.3.10 Software Request Register (DMASRR)
Write DMASRR to issue software DMA service requests. Software requests are subject to bus
control priority arbitration with all other software and har dware requests. A software request ac-
tivates the internal channel request signal. This signal remains ac tive until the channel completes
its buffer transfer (either by an expired byte count or an EOP# input). In the demand data-transfer
mode, a buffer transfer is suspended by deactivating the channel request signal. Because you can-
not deactivate the internal channel request signal before the end of a buffer transfer, you cannot
use software requests with demand data-transfer mode.
Figure 12-27. DMA Software Request Register (DMASRR – write format)
DMA Software Request (write format)
DMASRR Expanded Addr:
ISA Addr:
Reset State:
F009H
0009H
00H
7 0
———— —SR0CS
Bit
Number Bit
Mnemonic Function
7–3 — Reserved. These bits are undefined; for compatibility with future devices,
do not modify thes e bits.
2 SR Software Request:
Setting this bit generates a software request for the channel spe cified by
bit 0. When the channel’s buffer transfer completes, this bit is cleared.
1 0 Must be 0 for correct operation.
0 CS Channel Select:
0 = The selection for bit 2 affects ch annel 0.
1 = The selection for bit 2 affects ch annel 1.