User's Manual

Page 66 of 83

A Carrier Corp. Company

PART NUMBER T82002163

REV A

communications. The figure below illustrates a typical Omega TT4 Standard

Command exchange between the host and monitor:

Executes

Command

Echo back command

0x00 or parameters

Status

Any additional data

HOST PC MONITOR

TT4 PLUS

STANDARD

COMMAND

PROTOCOL

As can be seen in the diagram, the host initiates a command by sending a command value

to the monitor. The monitor then echoes back the same command value. This way

the host device will know that the unit received a specific command value correctly.

If the unit echoes back the wrong command value, the host computer merely ends

communications, thereby forcing the monitor to timeout.

If the host receives the correct command value back from the monitor, the host will send

either a 0h or command parameters. If a command requires parameters, such as the

“Write Scratchpad” command, the host computer upon receiving the echoed back

command would send the parameters at this time. For commands that do not require

any parameters, the host will send a 0h to act as a go signal.

Once the parameters or the 0h have been received, the monitor will then internally

execute the command and return a status byte followed by any additional data.

A status byte is always returned from the monitor upon completing a command whether

or not there is any additional data. The status byte is always a single byte value. A

0h value indicates successful completion of the command while a non-zero value