Datatech Enterprises 386/25, User Manual

Page: 127 / 141

Direct Memory Access
The VLSI-VL82C100 that encloses the 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 6-13: DMA Channels
DMA Channels
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 data
in 64KS blocks throughout the 1 g-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. Transfer
of 16-bit data between 16-bit adapters and 16bit 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.
2 4
Chapter 6: Appendix