Momentum Modbus Plus 170 PNT Series Guia do Utilizador descarregar pdf (Página 61)

Overview of Momentum M1 Processor Adapters

870USE10110 July 2004 61

Scan Time

Formula for

984LL Exec

The following formula applies to the M1E processor adapter with the 984LL exec.

Scan time = (0.25 ms/Ethernet device + 0.002 ms/word) + 0.13 ms/K of logic +

0.40 ms + MBPlustime

Example You have 50 ENT modules connected to a single M1E. The M1E has a configured

time of 50 ms each, a total of 4k user logic, and no MB+ card. The scan time for all

modules configured as fast as possible would be 12.5 ms + 0.52 ms + 0.40 ms =

13.42 ms. However, since the M1E will only communicate to 1/4 of the modules

(12.5 ms/50 ms = 1/4) on any given scan, the corrected average scan time would be

1/4 x (12.5) + 0.52 + 0.40 @ 4.1 ms.

Note:

Modbus Plus communications will slow the M1E. If there is no MB+ ring card,

then MBPlustime = 0.

If there is a MB+ ring card, then each scan will be extended 0.3 ms even if there

is no message.

Modbus Messages will add from 1 to 2 ms per scan, depending on the length of

the message.

Note:

The formula above presumes that all MSTR blocks and all configured

connections are set to go as fast as possible. In this case the M1E will attempt

to exchange data with each device once per scan.

If several devices are configured to communicate on a timed basis that is

substantially larger than the scan time calculated, then the communications to

those devices will be spread out over several scans.

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Momentum Modbus Plus 170 PNT Series Guia do Utilizador Página 61