Siemens ET 7Y Series Especificaciones descargar pdf (Pagina 148)

Functions of the IM 151-7 CPU

8-36

ET 200S IM 151-7 CPU Interface Module

A5E00058783-04

Global data communication

Global data communication enables the cyclic exchange of global data (e.g. I, O,

M) between SIMATIC S7-CPUs (unacknowledged data exchange). The data is

sent to all CPUs in the MPI subnetwork simultaneously by the CPU. The function is

integrated in the operating system of the IM 151-7 CPU.

Transmit and receive conditions

You should observe the following conditions for communication in GD circles:

 The following must apply for the sender of a GD packet:

Scan rate

Sender

x Cycle time

Sender

 60 ms

 The following must apply for the recipient of a GD packet:

Scan rate

Recipient

x Cycle time

Recipient

< Scan rate

Sender

x Cycle time

Sender

A GD packet could be lost if you do not observe these conditions. Reasons for this

are:

 the performance of the ”smallest” CPU in the GD circle

 global data is sent and received asynchronously by the sender and recipient

If in STEP 7 you set: ”Send After Each CPU Cycle” and the CPU has a short CPU

cycle (< 60 ms), the operating system could then overwrite a GD packet on the

CPU which has not yet been sent. The loss of global data is indicated in the status

field of the GD circle, provided that you have configured this option with STEP 7.

Scan rate

The scan rate indicates how many cycles the GD communication is divided into.

You can set the scan rate when configuring the global data communication in

STEP 7. If, for example, you select a scan rate of 7, global data communication

only occurs every 7 cycles. This relieves the load on the CPU.

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Siemens ET 7Y Series Especificaciones Pagina 148