Time Required For Communications - YASKAWA MP920 User Manual

6 217IF Module

6.3.3 Time Required for Communications

6.3.3

Time Required for Communications

This section explains the time required for signal transmissions between a Master and a
Slave, using the MEMOBUS protocol as an example.
Overview
The time required for communications between a Master and a Slave in a MEMOBUS sys-
tem may be roughly calculated from the time required for the following seven items:
• Transmission processing time by the Master for query message
• Delay time of the modem at the Master
• Transmission time for query message
• Processing time of the Slave
• Delay time of the modem at the Slave
• Transmission time for response message
• Processing time by the Master for response message
For the overall time required when multiple Slaves are connected to the port of the same
Master, calculate the time required for each Slave and then add these times.
Estimation of the Time Required for Each Item
The time required for each of the above seven items will now be explained in more detail.
Transmission Processing Time by the Master for Query Message
• This is the time it takes a computer to prepare a query message at the MEMOBUS port.
• The time taken depends on the processing time of each Master. With a Machine Control-
ler, the time depends on the scan time, and is normally one scan.
Delay Time of the Modem at the Master
• This is the time it takes the modem at the Master to return a clear to send (CTS) signal to
the Master once the request to send (RTS) signal has been received from the Master.
• With a Yaskawa Modem, this time can largely be ignored because it is less than 5 ms.
There is no delay time if a modem is not used.
Transmission Time for Query Message
• This is the time it takes the communications port of the Master to transmit the query
message.
• This time depends on the length of the query message and the baud rate, and can be cal-
culated using the following equation:
Transmisson time =
No. of characters in query message × No. of bits per character × 1000
6-8
Baud rate
(ms)