INT 14H
Encyclopedia

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
Modem
A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...

 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
Data set
A data set is a collection of data, usually presented in tabular form. Each column represents a particular variable. Each row corresponds to a given member of the data set in question. Its values for each of the variables, such as height and weight of an object or values of random numbers. Each...

 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
Framing error
Framing error can refer to the following:*Generally, a framing error is the result of starting to read a sequence of data at the wrong point.*In serial communications, a framing error is the result of reading a string of symbols which are grouped in blocks at the wrong starting point...

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
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x
OK