Message Handshake; Character Handshake; Command Mode; Multipoint - Omega DP41-B Series User Manual

Universal input

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7. Classes of Operation

7.1.1.1 MESSAGE HANDSHAKE

The RTS line from the host controller is checked when the device is ready to send

measurement data. If the RTS is true, it sends the complete message data without

interruption even if RTS goes false in the middle of transmission. If RTS is false, it

skips sending the data completely and continues with the next measurement.

The device checks the RTS input before sending each character and sends characters

only while RTS is true. It always completes sending the data before transferring the

latest reading to the output buffer.

In this mode, no handshake line is used, but instead a simple command from the host

requests that the device transmit its latest measurement message.

A device address from 0 to 199 is included in the COMMAND or RESPONSE

message. By using the addressing capabilities, collision on the bus can be avoided. If

"00" is used for the address on multiple units, they will all receive the COMMAND but

will not respond. This is used to avoid collisions on the bus. There are two (2) modes

available in the class; COMMAND MODE and ALARM MODE.

NO RTS handshaking is available with Multipoint.

7.2.1 COMMAND MODE

Each device, when it receives an addressed command, checks the received address.

If it matches its own pre-selected address, the device responds by fulfilling the

command. After a programmed turnaround delay time, it may transmit either an

acknowledgement and/or the requested data, or may have no response. If the

address does not match, the command is ignored. The programmed turnaround time

delay allows for line reflections to dissipate and for the transmitting host controller to

switch to the receive mode. The turnaround time delay choices are 0, 30, 100 and 300

milliseconds with a 3 ms uncertainty.

7-2

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