INT 14,5 - Extended Communication Port Control (PS/2 & later systems)

AH = 05

AL = read or write modem control register

= 00 read modem control register

= 01 read modem control register

DX = zero based serial port number (0-1) (0-3 for AT)

BL = modem control register

¦7¦6¦5¦4¦3¦2¦1¦0¦ BL

¦ ¦ ¦ ¦ ¦ ¦ ¦ +---- 1 = activate data terminal ready

¦ ¦ ¦ ¦ ¦ ¦ +----- 1 = activate request to send

¦ ¦ ¦ ¦ ¦ +------ OUT1

¦ ¦ ¦ ¦ +------- OUT2

¦ ¦ ¦ +-------- 0 = normal, 1 = loopback test

+------------- reserved, forced to zero

on return:

AH = port status

AL = modem status

BL = ~UART~ modem control register

- for status bits see ~INT 14,STATUS~