Compaq W4000 manual DMA Controller Registers, Register Controller

Chapter 4 System Support

DMA controller 1 can move up to 64 Kbytes of data per DMA transfer. DMA controller 2 can move up to 64 Kwords (128 Kbytes) of data per DMA transfer. Word DMA operations are only possible between 16-bit memory and 16-bit peripherals.

The RAM refresh is designed to perform a memory read cycle on each of the 512 row addresses in the DRAM memory space. Refresh operations are used to refresh memory on the 32-bit memory bus and the ISA bus. The refresh address is provided on lines SA00 through SA08. Address lines LA23..17, SA18,19 are driven low.

The remaining address lines are in an undefined state during the refresh cycle. The refresh operations are driven by a 69.799-KHz clock generated by Interval Timer 1, Counter 1. The refresh rate is 128 refresh cycles in 2.038 ms.

4.4.2.2DMA Controller Registers

Table 4-12 lists the DMA Controller Registers and their I/O port addresses. Note that there is a set of registers for each DMA controller.

Table 4-12.DMA Controller Registers

Table 4-12.

DMA Controller Registers

Register	Controller 1	Controller 2	R/W
Status	008h	0D0h	R
Command	008h	0D0h	W
Mode	00Bh	0D6h	W
Write Single Mask Bit	00Ah	0D4h	W
Write All Mask Bits	00Fh	0DEh	W
Software DRQx Request	009h	0D2h	W
Base and Current Address - Ch 0	000h	0C0h	W
Current Address - Ch 0	000h	0C0h	R
Base and Current Word Count - Ch 0	001h	0C2h	W
Current Word Count - Ch 0	001h	0C2h	R
Base and Current Address - Ch 1	002h	0C4h	W
Current Address - Ch 1	002h	0C4h	R
Base and Current Word Count - Ch 1	003h	0C6h	W
Current Word Count - Ch 1	003h	0C6h	R
Base and Current Address - Ch 2	004h	0C8h	W
Current Address - Ch 2	004h	0C8h	R
Base and Current Word Count - Ch 2	005h	0CAh	W
Current Word Count - Ch 2	005h	0CAh	R
Base and Current Address - Ch 3	006h	0CCh	W
Current Address - Ch 3	006h	0CCh	R
Base and Current Word Count - Ch 3	007h	0CEh	W
Current Word Count - Ch 3	007h	0CEh	R
Temporary (Command)	00Dh	0DAh	R
Reset Pointer Flip-Flop (Command)	00Ch	0D8h	W
Master Reset (Command)	00Dh	0DAh	W
Reset Mask Register (Command)	00Eh	0DCh	W

4-22Compaq Evo and Workstation Personal Computers

Featuring the Intel Pentium 4 Processor

Second Edition – January 2003