INT 14H

INT 14H, the serial communication interrupt

AH=00h init Comm Port
AH=01H Write Character
AH=02H Read Character
AH=03H Status Request
AH=04H Extended Init

AH=00h—init Comm Port

Prior to issuing INT 14H Upon returning from INT 14H
High Low High Low
AX 00h Comm Parm Byte AX Line Status Modem Status
BX BX
CX CX
DX Port Number (0=Com 1, 1=Com2, etc.) DX
Modem Status Byte—Low Byte
7 6 5 4 3 2 1 0 Description
x Received Line signal detect
x Ring Indicator
x data set ready
x clear to send
x Delta receive line signal detect
x Trailing edge ring detector
x delta data set ready
x Delta clear to send
Line Status Byte
7 6 5 4 3 2 1 0 Description
x Time-out Unpredictable results in other bits when this bit is set to 1
x Transmitter shift register empty
x Transmitter holding register empty
x Break detect
x Framing error
x Parity error
x Overrun error
x Data ready
Com Port Parameter Byte
7 6 5 4 3 2 1 0 Description Allowable Values
x x x Baud Rate
000=110 baud
001=150
010=300
011=600
100=1200(default)
101=2400
110=4800
111=9600
x x Parity
00=No parity
01=Odd
10=no
11=Even
x Stop Bits 0=1 stop bit
x x Word length
10=7 bits
11=8 bits

AH=01H—Write Character

Prior to issuing INT 14H Upon returning from INT 14H
High Low High Low
AX 01h character AX Line Status character
BX BX
CX CX
DX Port Number (0=Com 1, 1=Com2, etc.) DX

AH=02H—Read Character

Prior to issuing INT 14H Upon returning from INT 14H
High Low High Low
AX 02h AX Line Status character
BX BX
CX CX
DX Port Number (0=Com 1, 1=Com2, etc.) DX

AH=03H—Status Request

Prior to issuing INT 14H Upon returning from INT 14H
High Low High Low
AX 03h Comm Parm Byte AX Line Status Modem Status
BX BX
CX CX
DX Port Number (0=Com 1, 1=Com2, etc.) DX