Copyright(C) 1994 Terumasa KODAKA , Takeshi KONO


■RS-232C (AUX driver)
About RS-232C (AUX driver)
               o For the MS-DOS version referenced in this chapter, see the chapter "INT DCh MS-DOS Extended Function Call".

INT 19h - Function 00h (RSDRV)
Classification   RS-232C BIOS
Name             Initialization of RS-232C
                 Undocumented
Target           Normal + RSDRV.SYS
Input            AH=00h
                 DS=0060h
Output           AH=00h
                 AL,BX,CX,DX,DI,ES=Undefined
Explanation    o Initialize RS-232C in asynchronous mode.
               o Communication parameters follow the contents of 0060:0068h (WORD). The contents of memory switches 1 and 2 are copied to these two bytes at startup.
                 Also, when parameters are changed with the SPEED command, the settings are reflected.
               o The receive buffer is allocated 512 bytes (256 characters).
               u When RSDRV.SYS is installed, executing with DS ≠ 0060h executes BIOS INT 19h.
                 In MS-DOS (PS98-125 and earlier) where the AUX (RS-232C) driver is included in IO.SYS, executing with DS ≠ 0060h will cause the system to go out of control.
Related          0060:0068h
                 INT 19h - Function 00h (BIOS)
                 INT DCh - Function 0Ah


INT 19h - Function 01h (RSDRV)
Classification   RS-232C BIOS
Name             Sending data
                 Undocumented
Target           Normal + RSDRV.SYS
Input            AH=01h
                 DS=0060h
                 CL=Send data
Output           AH=00h
                 BX=Undefined
Explanation    o Sends 1 byte of data. Does not return until transmission is complete.
                 When the character length is 7 bits, SO and SI are added to codes of 80h and above.
               u When RSDRV.SYS is installed, executing with DS ≠ 0060h executes BIOS INT 19h.
                 In MS-DOS (PS98-125 and earlier) where the AUX (RS-232C) driver is included in IO.SYS, running with DS ≠ 0060h will cause the program to go out of control.
Related          INT 19h - Function 03h (BIOS)


INT 19h - Function 02h (RSDRV)
Classification   RS-232C BIOS
Name             Receiving data
                 Undocumented
Target           Normal + RSDRV.SYS
Input            AH=02h
                 DS=0060h
Output           AH=00h
                 AL=Received data
                 BX=Undefined
Explanation    o Takes one byte of received data from the receive buffer and outputs the received data and status. Does not return until data is received.
               u When RSDRV.SYS is installed, executing with DS≠0060h executes INT 19h of the BIOS.
                 In MS-DOS (PS98-125 and earlier) where the AUX (RS-232C) driver is included in IO.SYS, running with DS≠0060h causes the system to go out of control.
Related          INT 19h - Function 04h (BIOS)


INT 19h - Function 03h (RSDRV)
Classification   RS-232C BIOS
Name             Status acquisition
                 Undocumented
Target           Normal + RSDRV.SYS
Input            AH=03h
                 DS=0060h
Output           AH=00h
                 CL=8251A status
                   bit 7:DSR
                     1=ON
                     0=OFF
                   bit 6:BREAK
                     1=Detected
                     0=Not detected
                   bit 5:Framing error
                     1=Detected
                     0=Not detected
                   bit 4:Overrun error
                     1=Detected
                     0=Not detected
                   bit 3:Parity error
                     1=Detected
                     0=Not detected
                   bit 2:TxEMPTY
                     1=Transmit buffer empty
                     0=Transmit buffer full
                   bit 1:RxREADY
                     1=Received character
                     0=No received character
                   bit 0:TxREADY
                     1=Transmit ready
                     0=busy sending
                 BX,CH=undefined
Explanation    o Gets the current status of RS-232C.
               u When RSDRV.SYS is installed, executing with DS≠0060h executes BIOS INT 19h.
                 In MS-DOS (PS98-125 and earlier) where the AUX (RS-232C) driver is included in IO.SYS,
                 executing with DS≠0060h will cause the program to go out of control.
Related          INT 19h - Function 06h (BIOS)


INT 19h - Function 04h (RSDRV)
Category         RS-232C BIOS
Name             Get received data length
                 Undocumented
Target           Normal + RSDRV.SYS
Input            AH=04h
                 DS=0060h
Output           AH=00h
                 CX=number of received characters in receive buffer
                 BX=undefined
Explanation    o Checks the number of received characters stored in the receive buffer.
                 When RSDRV.SYS is installed, executing with DS ≠ 0060h will execute BIOS INT 19h.
                 In MS-DOS (PS98-125 and earlier) where the AUX (RS-232C) driver is included in IO.SYS,
                 executing with DS ≠ 0060h will cause the system to go out of control.
Related          INT 19h - Function 02h (BIOS)
                 INT DCh - Function 0Eh Subfunction 00h (Normal/High-Res)


INT 19h - Function 05~FFh(RSDRV)
Classification   RS-232C BIOS
Name             No function
                 Undocumented
Target           Normal + RSDRV.SYS
Input            AH=05~FFh
                 DS=0060h
Output           AH=00h
                 BX=Undefined
Explanation    o Returns without doing anything.
               u When RSDRV.SYS is installed, executing with DS≠0060h executes BIOS INT 19h.
                 In MS-DOS (PS98-125 and earlier) where the AUX (RS-232C) driver is included in IO.SYS,
                 running with DS≠0060h causes the system to go out of control.
Related