Online HelpPC 2.10 Quick Reference Utility Copyright 1991 David Jurgens
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
[helppc.bosbyte.nl] int 14,5