IBM PC CONVERTIBLE Technical Reference page 170

0020
0010
0001
0002
001E
0080
0000
0000
0001
0002
0003
0004
0005
0006
IE
52
56
57
51
53
8B F2
0008 8B FA
OOOA 01 E6
OOOC E8 0000 E
INTERRUPTS:
INTERRUPTS ARE ENABLE UPON ROUTINE ENTRY.
; **********************************
,
PUBLICS
; **********************************
PUBLI C COMMO_IO
PUBLI C PRLIO
PUBLIC COfLPOWER
; **********************************
,
EXTERNALS
; **********************************
DDS: NEAR EXTRN
EXTRN
EXTRN
EXTRN
EXTRN
EXTRN
BAUD_TABLE: BYTE
GELRTCREG: NEAR
GELVECTOR@:NEAR
Dll:NEAR
CHECLFOR_8250: NEAR
; **********************************
; EQUATES
; **********************************
DSR_BIT EQU 20H
CTS_B IT EQU lOH
DTR_BIT EQU 01H
RTS_BIT EQU 02H
RCLERR EQU OOOllllOB
DLAB EQU 80H
; **********************************
START OF CODE
; **********************************
PROC FAR
VECTOR TO APPROPRIATE ROUTINE
PUSH OS
PUSH OX
PUSH SI
PUSH 01
PUSH CX
PUSH BX
MOV SI,DX
MOV DI,DX
SHL
SI,l
CALL DDS
RECV ERROR BITS
DIVISOR LATCH ACCESS BIT
SAVE SEGMENT
AND REGISTERS USED
PORT NUMBER TO S I
AND 01
MAKE WORD OFFSET
BIOS DATA SEG INTO DS
OOOF 8B 94 0000
MOV OX, RS23LBASE [S I]
GET PORT BAS E ADDRESS
0013
OB 02 OR DX,DX
TEST FOR 0 (NO PORT)
0015 74 28 JZ A3 RETURN
0017 8A 08 MOV BL ,AL SAVE SEND CHAR IF IS ONE
;-----CHECK FOR PRESENSE OF 8250 AT THIS PORT
0019 83 C2 03 ADD DX,3 ADDRESS 8250 LINE CTRL REG
001C E8 0000 E CALL CHECLFOR_8250 CARRY SET IF PRESENT
001F FB STI SHIELDS DOWN
0020 72 05 JC AO YES, GO ON IF PRESENT
0022
80 CC 80 OR AH ,80H NO, SET TIMEOUT ERROR
0025 EB 18 JMP SHORT A3 EXIT
0027
83 EA 03 AO: SUB DX,3 RESTORE ADDRESS
002A 8A C3 AI: MOV AL, BL RESTORE SEND CHAR IF IS ONE
002C
OA E4 OR AH,AH TEST FOR AH=O
002E
74 16 JZ
A4
YES, COMMO INIT
0030 FE CC DEC AH TEST FOR AH= 1
0032 74 47 JZ A5 YES, S END CHAR
0034 FE CC
DEC AH
TEST FOR AH=2
0036 74 6C
JZ
A12
YES, RECEIVE CHAR
0038 FE CC
DEC
AH TEST FOR AH=3
003A
75 03 JNZ A3 NO, EXIT
003C E9 00C6 R JMP A18 YES, GET PORT STATUS
003F
A3: RETURN FROM RS232
003F 5B POP BX RESTORE REGISTERS
0040 59 POP
cx
ROM BIOS 2-145