Omron CS1W-DRM21, CJ1W-DRM21 operation manual 198

Message Communications Section 8-2

Shown below is the response time required to return data for 100 words.

•BYTE DATA READ request sending time: TBRS

DeviceNet header (4 bytes) + Parameters (3 bytes) = 7 bytes (no frag- ment)

Therefore, TBRS = 1 communications cycle time (TRM) = 3 ms

•PC’s processing time: TPC x 2

TPC x 2 = PC’s cycle time x 2 = 10 x 2 = 20 ms

•BYTE DATA READ response receiving time: TBRR

DeviceNet header (3 bytes) + Number of words to be read x 2 = 203 bytes Therefore, TBRR = 1 + 203 bytes/6 communications cycle time = 35 com- munications cycle time

•DeviceNet Unit refresh time: TRF = 2 ms

The message response time will be as follows:

=TRM + TPC x 2 + TRM x 35 + TRF x 2 =3+20+105+4

=132 ms

Shown below is the response time required to return data for 100 words to 8 clients.

•BYTE DATA READ request sending time: TBRS

DeviceNet header (4 bytes) + Parameters (3 bytes) = 7 bytes (no frag- ment)

Therefore, TBRS = 1 communications cycle time (TRM) = 3 ms

•PC’s processing time: TPC x 6 + TPC x 2 = TPC x 8

The following time is required to process data with other clients before the PC starts processing.

7 other clients/2 = Approximately cycle time x 3

If one processing requires twice the cycle time, the time will be as follows: Cycle time x 3 x 2 = Cycle time x 6

PC’s processing time: TPC x 2 = Cycle time x 2 Total time will be as follows:

Cycle time x 8

•BYTE DATA READ response receiving time: TBRR

DeviceNet header (3 bytes) + Number of words to be read x 2 = 203 bytes Therefore, TBRR = 1 + 203 bytes/6 communications cycle time = 35 com- munications cycle time

•DeviceNet Unit refresh time: TRF = 2 ms

The message response time will be as follows:

=TRM + TPC x 8 + TRM x 35 + TRF x 2 x 8 =3+80+105+32

=220 ms

Note The above equations can be used to find the approximate message response time, but this is the typical time, not the maximum time. The message response time will vary depending on the frequency of message communica- tions, the load on the remote node, the communications cycle time, and other factors. For any one DeviceNet Unit, the message communications time can be greatly increased due to heavy loads and the user program must be written to allow for this.

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