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 | ||||||||
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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 |
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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 | ||||||||
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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... |
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x | Parity error | |||||||
x | Overrun error | |||||||
x | Data ready |
Com Port Parameter Byte | |||||||||||||||||
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7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | Description | Allowable Values | ||||||||
x | x | x | Baud Rate |
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x | x | Parity |
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x | Stop Bits | 0=1 stop bit | |||||||||||||||
x | x | Word length |
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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 |