6. DMA Controller
65
REGISTER:
ADDRESS:
AT ADDRESS:
ACCESS:
D7
D6
D5
D4
D3
D2
D1
D0
---
0F01Bh
0
0
0
0
0
0
0
0
DMAMOD2
W/O, D0 specifies channel
1= Bits D7-D2 affect channel 1
0= Bits D7-D2 affect channel 0
Reserved
1= Channel target address hold
0= Channel target address will increment or decrement
1= Channel requestor address will hold
0= Channel requestor address will increment or decrement
1= Channel target is in I/O space
DMA mode register 2
0= Channel target bit 0 is in memory space
1= Channel requestor address decrement
0= Channel requestor address increment
1= Channel target is in I/O space
0= Channel target bit 0 is in memory space
1= Fly-by data transfer (required for backplane ZT 8954 floppy support)
0= Two-cycle data transfer (required for local floppy support)
DMA Mode Register 2
DMA Software Request Register
Use the DMASRR register write format 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 activates the internal channel request
signal. This signal remains active until the channel completes its buffer transfer. In the
demand data-transfer mode, a buffer transfer is suspended by deactivating the channel
request signal. Because you cannot deactivate the internal channel request signal
before the end of a buffer transfer, you cannot use software requests with demand data-
transfer mode.
Use the DMASRR register (read format) to determine if a software request for a
particular channel is pending.
REGISTER:
ADDRESS:
AT ADDRESS:
ACCESS:
D7
D6
D5
D4
D3
D2
D1
D0
0009h
Read format
1= Channel 0 has a software request pending, read this register to clear
0= No software request pending for channel 0
1= Channel 1 has a software request pending, read this register to clear
0= No software request pending for channel 1
Reserved
DMASRR
0F009h
DMA software request register
Reserved
0
0
DMA Software Request Register