Intel 80C188EC User Manual page 323

DIRECT MEMORY ACCESS UNIT
$mod186
name DMA_WITH_SCU
; The following example initializes the DMA unit to perform
; DMA-driven serial transfers.
;
; It is assumed that the serial port has been initialized for
; Mode 1 asynchronous transfers. Register mnemonics are assumed
; to be defined elsewhere in EQUate instructions.
DATA SEGMENT
XMIT_BUFF DB 'This is a serial message.'
RECV_BUFF DB 128 DUP('ReCv')
DATA ENDS
CODE SEGMENT
ASSUME CS:CODE
MOV
MOV
ASSUME DS:DATA
; First we set up DMA channel 2 (Module B, channel 0) to handle
; transmit requests from serial port 1.
;
; The source of data is the transmit buffer in memory.
; The destination for data is the TBUF register for serial port 1...
MOV AX, SEG XMIT_BUFF
ROL AX, 4
MOV BX, AX
AND AX, 0FFF0H
ADD AX, OFFSET XMIT_BUFF+1
; USE XMIT_BUFF+1 BECAUSE FIRST BYTE IS SENT MANUALLY.
; NOW LOW BYTES OF POINTER ARE IN AX.
ADC BX, 0
AND BX, 000FH
MOV DX, D2SRCL
OUT DX, AX
MOV DX, D2SRCH
MOV AX, BX
OUT DX, AX
; SOURCE POINTER DONE. DESTINATION IS IN PCB.
MOV DX, D2DSTL
MOV AX, S1TBUF
OUT DX, AX
10-34
AX, DATA
DS, AX
Example 10-2. DMA-Driven Serial Transfers
; JUNK DATA
; DATA SEGMENT POINTER
; GET HIGH 4 BITS
; SAVE ROTATED VALUE
; GET SHIFTED LOW 4 NIBBLES
; ADD IN THE CARRY
; TO THE HIGH NIBBLE
; GET JUST THE HIGH NIBBLE
; AX=LOW 4 BYTES
; GET HIGH NIBBLE
; TRANSMIT BUFFER FOR
; CHANNEL 1 IS DEST