(SYNC)ASYNC1

0 45678ASCII 1()() 11.52 1

120/10101201200/1200

2

(bit)HDLC()EBCDASCIIIBM(BSC)

a b c

(1)(2) ABBA(3)

1

2(MODEM)()

(DTE)MODEM(DCE)1RS-232C RS-232CD259

RS-232CMODEMRS-232C

RS-232C259. TXD2MODEM RXD3RTS*4MODEMCTS*5

DSR*6(MODEM) CD8()MODEM RI22MODEMDTR*20RIMODEMGND7

RS-232CEIA1-3V~-15v0+3V~+15V EIATTL MCl488TTLEIAMCl489EIAITLRS-232C

2RS-423ARS-232CRS-232C1987RS-423A RS-423A

3RS-422ARS-422A

RS-422A2v0.2v25v

4RS-485RS-485

12RS-232C3RS-232CTTL4Modem

8251A8251A8251A 8251A 8251A8251A

8251A8251A8251A10~64K0~19.2K256788251A/

35678116641/11152 45

8251A

1 TXD12

CPU8251ATXRDYCPU8CPUTXE

2RXDRXD 8251ARXRDYCPU

8251ARXDRXD8251ASYNDET

SYNDET RXDRXRDY

3 CPU8251A38CPU8251ACPU8251A

4/(1)8251A(2)8251A (3)/C/ (4)CLK8251A RESET8251A58251A

251A

1251ACPU CS*CPUD7-D08CPU8251A8251ACPU

/RD* CPU8251AWR* CPU8251AC/D*//8251A/RD*WR*C/D*38251A

(4) TXRDYCPU8251A TXETXE8251A RXRDY8251ACPURXRDYRXRDY SYNDET

28251A(1) DTR*CPU DSR* RTS*CPU CTS*8251A43

TXDCPU8251ATXD RXD8251A

3 CLK8251A304.5 TXDTXCTXC11664

RXD:TXCRXCTXCCLK VCC GND

8251ACPU8251ACPU

2

8251A MOV DX0FFF2H L IN ALDX AND AL02H Dl1 JZ L MOV DX OFFF0H IN Al DX

48251A 128251A(3) CPU

8251A1 8251A()167/200E2H00E4H11111010B 0FAH00110111B 37H

MOV AL 0FAH MOV DX00E2HOUT DX AL 7/2 MOV AL37H OUT DX AL RTS*DTR*

2 52H216H7/00111000B 38H10010111B 97H8251A38251A8251ACPU

MOV AL38H 2OUT 52HAL 7MOV AL16H OUT 52HAL 16HOUT 52HAL MOV AL 97H OUT 52H AL

3 8251A80 8251A52H50HBUFFER

MOV AL0FAH 16 OUT 52HAL 72 MOV AL35H OUT 52HAL MOV DI0 MOV CX80 80

BEGININ AL52H RXRDY10TEST AL02H JZ BEGIN IN AL50 MOV DXOFFSET BUFFERMOV [DX+DI]ALINC DI IN AL52H TEST AL38H /

JZ ERROR LOOP BEGIN JMP EXIT 80ERROR CALL ERR-OUT EXIT

48251A

CPUTXRDY8251ACPURXRDY8251A

STT MOV DX8251A MOV AL7FH OUT DXAL 825lA81 MOV AL11H 64OUT DXALMOV DI MOV CX

NEXTMOV DX8251A IN ALDX AND AL01H TXRDY? JZ NEXT MOV DX8251A MOV AL[DI]8251A OUT DXAL INC DI LOOP NEXT HLT

SRRMOV DX8251A MOV AL7FH OUT DXAL 8251A8MOV AL 14H 164OUT DXAL MOV DI MOV CX

COMT MOV DX8251A IN ALDX ROR AL1 RXRDY? ROR AL1 JNC COMT ROR AL1 ROR AL1 JC ERR

MOV DX8251A IN ALDX MOV [DI]AL INC DI LOOP COMT HLT ERR CALL ERR-OUT

182512825138251

48251716482513FBH/3F8H58251A38.4KHzRTS*CTS*8251A02C0H02C1H71600B/s816H

I/OCPUI/OI/O CPUI/O/CPU

1/CPU/

2/////

I/O1CPUI/O CPU(READY)BUSY CPU

2I/OCPUI/OCPUI/OCPU

/CPU//

3.CPU/I/0(M/IO*)1-2/

12CPU

8255A 8255A8255A8255A

Intel 8255AI/OIntel

8255A8255A1ABC I/OA8I/O/B8I/OC8I/O4I/O

8255A

2ABCPU8255ACPU8255AC/AAC4BBC4

388255A/CPU8255A4//8255ARESETA0A1

8255ACPU1CPUD0-D78RESET8255AABC

CS*RD*8255ACPUWR*CPU8255AA1A08255A8255A4ABC

8255A

2 PA0~PA7 PB0~PB7 PC0~PC7 8255A 8255A0/ABC1/A B2/A

10/ABCI/O0

21 I/OAB8I/OC6AB20 (1) 1CPC3-PC5APC0-PC2BPC6~PC70

1

STB*8255AIBFSTBINTRINTRSTBIBFINTEINTEAPC4BPC0 ABSTB* PC4PC2IBFPC5PC1INTR PC3PC0INTE PC41PC21

(2) 1

OBF*CPU8255A8255AACK*OBF*8255AINTRINTRACKOBFINTEINTEAPC6BPC2 A BOBF* PC7 PC1ACK* PC6 PC2INTR PC3 PC0INTE PC61 PC21

32I/OAC5A30B121

12 STB* PC4IBFPC5OBF*PC7ACK* PC6INTR PC3(2) 22

(3) 2 20 11XXX01T 2011XXX00T 2111XXX11X 2111XXX10X XT10

8255A18255A8255AC/18255A8255A

8255A

1 8255AA0B0C40C40 10010001 91H MOV AL 91H OUT CTRL_PORTAL(2) C//1/

/

A2 PC4PC6B1PC2 MOV AL0C4H OUT CTRL_PORTAL MOV AL09H OUT CTRL_PORTALPC4A MOV ALODH OUT CTRL_PORTALPC6A MOV AL 05HOUT CTRL_PORTALPC2B

23 8255AA0BUFFCPU8088

BUSYACKBUSY

PC0PC0/PC7BUSY8255A10001000 88H A0C00PC0: 00000001 01HPC000000000 00H8255A400H01H02H03H

DADA SEGMENTBUFF DB 'This is a print program!''$'DATA ENDSCODE SEGMENT ASSUME CSCODE DSDATASTARTMOV AX DATA MOV DS AX MOV SIOFFSET BUFF

MOV AL 88H A0OUT 03H AL C00MOV AL 01HOUT 03HAL PC0WAIT IN AL 02H TEST AL 80H JNZ WAIT MOV ALSI CMP AL'$' JZ DONE OUT 00HAL A

MOV AL00H OUT 03H AL MOV AL 01H OUT 03HAL INC SI JMP WAITDONE MOV AL0DH OUT 00HAL MOV AL 00H OUT 03HAL MOV AL 01H OUT 03HAL

WAIT1 IN AL 02HTEST AL 80H PC71 JNZ WAIT 1 MOV AL0AH OUT 00HAL MOV AL 00H OUT 03HAL MOV AL 01H OUT 03HAL MOV AH4CH INT 21H CODE ENDSEND START

4 8255A1BUFF100CentronicsPC08255AA8255APC38259AIR3

8255A1010XXX0 PC0: 00000001 01HPC0 00000000 00HPC6: 00001101 0DH 8255AA8255A400H01H02H03H8259AICW208H A0BH2CH4

MAIN MOV AL0A0H OUT 03HAL 8255A MOV AL01H OUT 03HAL XOR AXAX MOV DSAX MOV AXOFFSET ROUTINTR MOV WORD PTR [002CH]AX MOV AXSEG ROUTINTR

MOV WORD PTR [002EH]AX MOV AL0DH OUT 03HAL 8255A A MOV DIOFFSET BUFF MOV CX99 MOV AL[DI] OUT 00HAL INC DI MOV AL00H OUT 03HAL

INC AL OUT 03HAL STI NEXT HLT LOOP NEXT HLT

ROUTINTRMOV AL[DI] OUT 00HAL A MOV AL00H OUT 03HAL INC AL MOV 03HAL INC DI IRET

18255A01228255AA2B

38255AA0B1C080H~83H48255AA0B0 8255AA1A0CPU8086A2A1A7A6A5A4A3=101008255A