User's Manual

Page 65 of 83

A Carrier Corp. Company

PART NUMBER T82002163

REV A

In the case above where the host computer correctly receives a 0h back from the monitor,

the host will then send the final 4-byte login sequence to the monitor. The final

sequence of 4 bytes is 7Ah, 5Eh, 8Ah, and A1h. The monitor should receive the 4

values from the host computer and verify whether or not they are correct. If it

determines the values were received correctly, it will send back a 1-byte value of 0h.

If the monitor receives any of the bytes incorrectly, it will terminate the login process,

return to what it was doing, and wait for the host to start the whole login process over.

If the host does not retry, then the monitor will timeout after approx. 1 minute and

will ignore any attempts by the host to communicate with it. At this point it would be

necessary to re-enable the communications mode and start the whole connection

process over again. This last action of sending 4 consecutive bytes accomplishes two

goals. It again verifies that the unit is indeed receiving data at the correct baud rate

and it acts as a simple password against any bogus communications attempts.

Once the host PC has successfully logged in and has established a connection with the

monitor. The host PC may now send predefined commands to the monitor, which

allows it to do things such as, configure the monitor or download the data. The

command protocol and a list of the commands with their definitions are described in a

later section. It is also important to note that once a connection has been established,

a 15-minute timeout timer is established within the monitor in place of the 1-minute

timeout timer. This timer is used as a count down timer that determines the timeout

period for communications between the monitor and host PC. Effectively what this

means is that as long as this timer is refreshed and not allowed to expire,

communications mode will stay active allowing commands to be sent. The monitor

refreshes this timer any time valid command is sent, so as long as commands continue

to be sent, the monitor will continue to refresh the timer. If no commands are sent to

the monitor within 15 minutes, communications mode within the monitor will be

terminated. The reason for the 15-minute timeout timer is to maximize the battery

life of the monitor. Because of the power drain associated with the communications

mode, if the communications mode were allowed to continue indefinitely, the battery

would be drained very quickly. A battery that would last a year under normal

operation may only last a few days if the communications mode were enabled

continuously.

Command Protocol

The Omega TT4 command protocol is based on a Command/Response type architecture.

This approach works on the principle were the host is in charge of the

communications session and issues commands for the monitor to act on. The Omega

TT4 supports all of the same commands as its predecessor the TT4 (which will be

referred to as “Omega TT4 Standard Commands”) as well as new commands

(referred to as “Omega TT4 Extended Commands”), which use the same basic format

with the exception that the command parameters and return data are in packet format

with a checksum. This packet format was implemented to increase the speed of the