Epson Apex 386SX/16 Canadian Product User Manual - Page 119

Direct, Memory, Access, Channel

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Direct Memory Access Eight DMA channels are supported by the system. Two Intel 8237-5 DMA controller chips (four channels in each chip) are used to provide eight DMA channels. The DMA channels are assigned as follows: Table 6-5: DMA Channels DMA Channel Channels 0 through 3 are contained in DMA controller 1. Transfers of 8-bit data, 8-bit I/O adapters and 8-bit or 16-bit system memory are supported by these channels. Each of these channels will transfer in 64KB blocks throughout the 16-megabyte system address space. Channels 4 through 7 are contained in DMA controller 2. To cascade channels 0 through 3 to the microprocessor, use channel 4. Transfers of 16-bit data between 16-bit adapters and 16-bit system memory are supported by channels 5, 6 and 7. DMA channels 5 through 7 will transfer data in 128KB blocks throughout the 16-megabyte system address space. These channels will not transfer data on odd-byte boundaries. Chapter 6: Appendix 21

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Direct
Memory
Access
Eight
DMA
channels
are
supported
by
the
system.
Two
Intel
8237-5
DMA
controller
chips
(four
channels
in
each
chip)
are
used
to
provide
eight
DMA
channels.
The
DMA
channels
are
assigned
as
follows:
Table
6-5:
DMA
Channels
DMA
Channel
Channels
0
through
3
are
contained
in
DMA
controller
1.
Transfers
of
8-bit
data,
8-bit I/O
adapters
and
8-bit
or
16-bit
system
memory
are
supported
by
these
channels.
Each
of
these
channels
will
transfer
in
64KB
blocks
throughout
the
16-megabyte
system
address
space.
Channels
4
through
7
are
contained
in
DMA
controller
2.
To
cascade
channels
0
through
3
to
the
microprocessor,
use
channel
4.
Transfers
of
16-bit
data
between
16-bit
adapters
and
16-bit
system
memory
are
supported
by
channels
5, 6
and
7. DMA
channels
5
through
7
will
transfer
data
in
128KB
blocks
throughout
the
16-megabyte
system
address
space.
These
channels
will
not
transfer
data
on
odd-byte
boundaries.
Chapter
6:
Appendix
21