Software Request Register (Dmasrr); Dma Software Request Register (Dmasrr – Write Format) - Intel 386 User Manual

Intel386™ EX EMBEDDED MICROPROCESSOR USER'S MANUAL

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 hardware requests. A software request ac-
tivates the internal channel request signal. This signal remains active 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.
DMA Software Request (write format)
DMASRR
7
— —
Bit Bit
Number Mnemonic
7–3 —
2 SR
1 0
0 CS
Figure 12-27. DMA Software Request Register (DMASRR – write format)
12-42
— —
Reserved. These bits are undefined; for compatibility with future devices,
do not modify these bits.
Software Request:
Setting this bit generates a software request for the channel specified by
bit 0. When the channel's buffer transfer completes, this bit is cleared.
Must be 0 for correct operation.
Channel Select:
0 = The selection for bit 2 affects channel 0.
1 = The selection for bit 2 affects channel 1.
Expanded Addr: F009H
ISA Addr: 0009H
Reset State: 00H
— SR
Function
0
0 CS