User's Manual

Page 63 of 83

A Carrier Corp. Company

PART NUMBER T82002163

REV A

Establishing a Connection

During normal monitor operation, communications mode is disabled. There are two

ways to enable the monitor’s communications mode. The first method is for an

external device to trigger the monitor’s internal reed switch by means of a magnet. If

this approach is used, the magnet must keep the reed switch triggered during the

entire communications session. The second method is to enable the communications

mode by means of the communications enable pin on the J2 connector located inside

the monitor. This pin must be pulled to ground and held there during the entire

communications session.

Once the monitor has entered communications mode, the host PC is responsible for

establishing a connection with the monitor. If the host PC does not establish a

connection within one minute’s time, the microcontroller within the monitor will

disable communications mode thus terminating communications. If this occurs, it

will be necessary to re-enable the communications mode by either re-triggering the

reed switch by removing it from the magnet for approximately 500msec and then

placing it back near the magnet or by pulling the communications enable pin high for

approximately 500msec and then back to ground.

To establish a connection with the monitor, the host PC must send a sequence of

Bytes to the monitor and receive the correct responses back from the monitor. This

sequence is designed to give the monitor time to wake-up and allow the host to log in.

If any of the bytes are sent or received incorrectly or at the wrong time during the

connection attempt, both the host and monitor should assume bad communications

and return to their previous states. The following table shows the steps that are taken

to connect to the monitor: