Int 14H [PS/2] Function 05H Extended communications port control

Reads or sets the modem control register (MCR) for the specified serial communications port.

Call with:

AH = 05H

AL = subfunction

00H to read modem control register

01H to write modem control register

BL = modem control register contents (if AL = 01H)

Bit(s) Significance

0 data-terminal ready

1 request-to-send

2 Out1

3 Out2

4 loop (for testing)

5—7 reserved

DX = communications port number (0 = COM1, 1 = COM2, etc.)

Returns:

If called with AL = 00H

BL = modem control register contents (see above)

If called with AL = 01H

AH = port status (see Int 14H Function 00H)

AL = modem status (see Int 14H Function 00H)