Intel 386 - Manual (Page 370)

12-35
DMA CONTROLLER
12.3.5 Command 1 Register (DMACMD1)
Use DMACMD1 to enable both channels and to select the rotating method for changing the bus
control priority structure.
Figure 12-22. DMA Command 1 Register (DMACMD1)
DMA Command 1
DMACMD1
(write only) Expanded Addr:
ISA Addr:
Reset State: F008H
0008H
00H
7 0
— — — PRE — CE — —
Bit
Number
Bit
Mnemonic
Function
7–5 — Reserved; for compatibility with future devices, write zeros to these bits.
4 PRE Priority Rotation Enable:
0 = Priority is fixed based on value in DMACMD2.
1 = Enables the rotation method for changing the bus control priority
structure. That is, after the external bus master or one of the DMA
channels is given bus control, it is assigned to the lowest priority
level.
3 — Reserved; for compatibility with future devices, write zero to this bit.
2 CE Channel Enable:
0 = Enables channel 0 and 1.
1 = Disables the channels.
1–0 — Reserved; for compatibility with future devices, write zeros to these bits.