SC>
  > The PMLM program that comes with SIO is a "Poor Man's Line
  > Monitor" that is able to show you what is happening on the
  > serial ports. It's a great little tool.
  >
  > But it got me wondering how it's done.
SC>

  The easiest *official* way to monitor a character device is to install
  a device monitor (if, of course, the device supports this).

  There are some back-door device drivers in SIO.SYS ($SIO$n, where n is
  a digit), but their interface is unpublished (and rightly so).  PMLM
  appears to use these.

  > JdeBP <
___
 X MegaMail 2.10 #0:
--- Maximus/2 3.00