Intel 386 - Manual (Page 381)

Intel386™ EX EMBEDDED MICROPROCESSOR USER’S MANUAL
12-46
12.3.12 Bus Size Register (DMABSR)
Use DMABSR to determine the requester and target data bus widths (8 or 16 bits).
Figure 12-31. DMA Bus Size Register (DMABSR)
DMA Bus Size
DMABSR
(write only) Expanded Addr:
ISA Addr:
Reset State: F018H
—
X1X10000B
7 0
— RBS — TBS — — 0 CS
Bit
Number
Bit
Mnemonic
Function
7 — Reserved; for compatibility with future devices, write zero to this bit.
6 RBS Requester Bus Size:
Specifies the requester’s data bus width for the channel specified by bit
0.
0 = 16-bit bus
1 = 8-bit bus
5 — Reserved; for compatibility with future devices, write zero to this bit.
4 TBS Target Bus Size:
Specifies the target’s data bus width for the channel specified by bit 0.
0 = 16-bit bus
1 = 8-bit bus
3–1 0 Must be 0 for correct operation.
0 CS Channel Select:
0 = The selections for bits 7–4 affect channel 0.
1 = The selections for bits 7–4 affect channel 1.