Intel 80C188XL Register NameDMA Source Address Pointer High, Register Mnemonic DxSRCH, DMA Xxxxh

DIRECT MEMORY ACCESS UNIT

Two 16-bit Peripheral Control Block registers define each of the 20-bit pointers. Figures 10.7 and

10.8show the layout of the DMA Source Pointer address registers, and Figures 10.9 and 10.10 show the layout of the DMA Destination Pointer address registers. The DSA19:16 and DDA19:16 (high-order address bits) are driven on the bus even if I/O transfers have been pro- grammed. When performing I/O transfers within the normal 64K I/O space only, the high-order bits in the pointer registers must be cleared.

Register Name:DMA Source Address Pointer (High)

Register Mnemonic: DxSRCH

Register Function:Contains the upper 4 bits of the DMA Source pointer.

15				0
	D	D	D	D
	S	S	S	S
	A	A	A	A
	1	1	1	1
	9	8	7	6

A1185-0A

Bit	Bit Name	Reset	Function
Mnemonic		State
DSA19:16	DMA	XXXXH	DSA19:16 are driven on A19:16 during the
	Source		fetch phase of a DMA transfer.
	Address

NOTE: Reserved register bits are shown with gray shading. Reserved bits must be written to a logic zero to ensure compatibility with future Intel products.

Figure 10-7. DMA Source Pointer (High-Order Bits)

10-11