Intel 80C186XL Direct Memory Access Unit, Example 10-1.Initializing the DMA Unit Continued

DIRECT MEMORY ACCESS UNIT

MOV	DX, D0DSTH
MOV	AX,	BX	; GET HIGH NIBBLE
OUT	DX,	AX

; THE POINTER ADDRESSES HAVE BEEN SET UP. NOW WE SET UP THE TRANSFER COUNT.

MOV	AX, 29		;	THE MESSAGE IS	29 BYTES LONG.
MOV	DX,	D0TC	;	XFER COUNT REG
OUT	DX,	AX

;NOW WE NEED TO SET THE PARAMETERS FOR THE CHANNEL AS FOLLOWS:

;	DESTINATION	SOURCE
;	-----------	------

;MEMORY SPACE MEMORY SPACE

;INCREMENT PTR INCREMENT PTR

;TERMINATE ON TC, NO INTERRUPT, UNSYNCHRONIZED, LOW PRIORITY RELATIVE

;TO CHANNEL 1, BYTE XFERS. WE START THE CHANNEL.

MOV AX, 1011011000000110B

MOV DX, D0CON

OUT DX, AX

;THE UNSYNCHRONIZED BURST IS NOW RUNNING ON THE BUS...

;NOW SET UP CHANNEL 1 TO SERVICE THE DISK CONTROLLER.

;FOR THIS EXAMPLE WE WILL ONLY BE READING FROM THE DISK.

;THE SOURCE IS THE I/O PORT FOR THE DISK CONTROLLER.

MOV	AX, DISK_IO_ADDR
MOV	DX, D1SRCL
OUT	DX, AX	; PROGRAM LOW ADDR
XOR	AX, AX
MOV	DX, D1SRCH	; HI ADDR FOR IO=0
OUT	DX, AX

; THE DESTINATION IS THE DISK BUFFER IN MEMORY

MOV	AX, SEG DISK_BUFF
ROL	AX, 4		; GET		HIGH 4 BITS
MOV	BX, AX		;	SAVE ROTATED VALUE
AND	AX,	0FFF0H	;	GET	SHIFTED LOW	4 NIBBLES
ADD	AX,	OFFSET DISK_BUFF

; NOW LOW BYTES OF POINTER ARE IN AX

ADC	BX, 0	; ADD IN	THE CARRY
		; TO THE	HIGH NIBBLE
AND	BX, 000FH	; GET JUST		THE HIGH NIBBLE
MOV	DX, D1DSTL
OUT	DX, AL	; AX=LOW	4	BYTES
MOV	DX, D1DSTH
MOV	AX, BX	; GET HIGH		NIBBLE
OUT	DX, AX

;THE POINTER ADDRESSES HAVE BEEN SET UP. NOW WE SET UP THE TRANSFER COUNT.

Example 10-1. Initializing the DMA Unit (Continued)

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