Schneider Electric LUFP9 Appendix B Default Configuration, Configuring Modbus exchanges, 16#10

8. Appendix B: Default Configuration

The configuration described below corresponds to the LUFP9 gateway’s default configuration.

This chapter mainly gives the user information about the performances obtained on the downstream Modbus network. It allows the user to decide whether, for example, he should change the period for cyclical exchanges with one or more of the TeSys U motor starters (see chapter 6 Configuring the Gateway, page 40).

8.1. Configuring Modbus exchanges

The LUFP9 gateway carries out four types of exchanges with each of the 8 TeSys U motor starters. The first two exchanges are cyclical and allow you to control and monitor the motor starter. The last two exchanges are aperiodic (only when there is a change in the values of the data to be transmitted to the motor starter) and allow you to read and change the value of any motor starter parameter.

Function	Modbus function	Number of	Exchange between the LUFP9 gateway
		bytes (1)	and the TeSys U motor starter
16#03	Read Holding	11,5 + 10,5	Periodic reading (300 ms period) of the	TeSys U	motor
	Registers		starter’s status register (address 455 = 16#01C7) only
16#10	Preset Multiple	14,5 + 11,5	Periodic writing (300 ms period) of the	TeSys U	motor
	Registers		starter’s status register (address 704 = 16#02C0) only
	(Read Holding		Aperiodic reading of the value of a single parameter, for a
(16#03)		11,5 + 10,5	single TeSys U motor starter at a time	(function and
	Register)
			address supplied by the user)
	(Preset Single		Aperiodic writing of the value of a single parameter, for a
(16#06)		11,5 + 11,5	single TeSys U motor starter at a time	(function and
	Register)
			address and value supplied by the user)

(1)Number of bytes in the Query + number of bytes in the Response, plus a period of silence of 3.5 characters for each of these two frames (see description of the “Message delimiter (10ms)” parameter in chapter 6.12.3 “Sub-Network” Element, page 77). Each byte will be transmitted in the form of a group of 10 bits (8 data bits, 1 start bit and 1 stop bit). These values allow you to calculate the approximate amount of traffic on the downstream Modbus network as follows:

Volume of periodic traffic (300 ms period)	[ (11.5 + 10.5) + (14.5 + 11.5) ] × (8 + 1 + 1) = 480 bits
For 1 TeSys U motor starter	1 × 480 × (1,000 ÷ 300) =	1,600 bits/s
For 8 TeSys U motor starters	8 × 480 × (1,000 ÷ 300) =	12,800 bits/s

As a result, on a network operating at 9,600 bits/s, you will need to considerably increase the cycle time for all or part of the periodic Modbus commands. On the other hand, at a speed of 19,200 bits/s (default speed), the available bandwidth is sufficient to allow proper communications, even in occasional degraded mode (frames re-transmission), and to allow the use of aperiodic setup exchanges.

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