80C186EC/80C188EC Microprocessor User's Manual

DIRECT MEMORY ACCESS UNIT
XOR AX, AX ; HIGH ADDRESS=0
MOV DX, D3SRCH
OUT DX, AX
; THE POINTER ADDRESSES HAVE BEEN SET UP. NOW WE SET UP THE TRANSFER COUNT.
MOV AX, 128 ; INTERRUPT AFTER 128 BYTES
MOV DX, D3TC ; ARE RECEIVED.
OUT DX, AX
; NOW WE NEED TO SET THE PARAMETERS FOR THE CHANNEL AS FOLLOWS:
;
; DESTINATION SOURCE
; ----------- ------
; MEMORY SPACE I/O SPACE
; INCREMENT PTR CONSTANT PTR
;
; TERMINATE ON TC, INTERRUPT, SOURCE-SYNCHRONIZED, HIGH PRIORITY
; RELATIVE TO CHANNEL 1, BYTE XFERS. INTERNAL DRQ. ARM CHANNEL.
MOV
MOV
OUT
AX, 1010001101110110B
DX, D3CON
DX, AX
; AT THIS POINT THE DMA UNIT WILL HANDLE SERIAL RECEPTIONS,
; AS LONG AS THE SERIAL PORT HAS BEEN INITIALIZED.
; NOW START THE BURST TRANSMIT ("PRIME THE PUMP")
MOV AL, XMIT_BUFF ; GET FIRST BYTE
XOR AH, AH ; CLEAR RESERVED BITS
MOV DX, S1TBUF ; TRANSMIT IT
OUT DX, AX
; BURST TRANSMIT HAS BEGUN.
CODE
ENDS
END
Example 10-2. DMA-Driven Serial Transfers (Continued)
10-36