The X 86 Microprocessors: Architecture, Programming and Interfacing (8086 to Pentium) 2nd Edition by Pearson

11-36

THE

x86 MICROPROCESSORS

iii) Channel 2 for floppy disk controller.

iv) Channel 3 for hard disk controller.

Remember that the 8237 has only a 16-bit address bus capability; hence, for the addresses

beyond 64KB, the extra bits are provided by a page register, which is a latch for holding

the extra address bits.

11.7.1 | DMA and PC-AT

With the advent of the ISA bus for PC-AT type computers, two DMA controllers came

to be used. Two Intel 8237-DMA controllers were cascaded together, and each chip had

four channels. Channel allocation was as follows:

0 DRAM Refresh (obsolete),

1 User hardware,

2 Floppy disk controller,

3 Hard disk (obsolete), ...