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Chapter 2 Specification of Communication port for CPU module

2 – 40

(1) 1: N communication (RS-485)

(A) Precautions

When performing 1 to N communication using RS-485, communicate in polling/selecting mode. When

creating a ladder program, note the following points.

[1] Communicate by making sure the master station and slave station are using the same start code.

[2] The master station should transmit a request by specifying the station number of the slave station.

[3] The slave station should transmit a response only when the request from the master station is to the

own station. Set the station so that it will reset the mode and wail for the next request in the event is

received a request addressed to other station.

[4] The master station should transmit a new request after at least 20 ms (t

in figure below) has elapsed

from the time it completed receiving the last response from the slave station.

[5] The slave station should transmit a request after at least 20 ms (t

in figure below) has elapsed from the

time it completed receiving the request from the master station.

An example of 1 to N transmission sequence is shown below. This example shows a sequence in which the

master station transmits a series of requests to the slave stations 1 to 3, and a sequence in which the slave

station received the request transmits the response.

In Fig.2.28, a salient expressed in solid line indicates that the station received a transmission addressed to the

own station, and a salient expressed in dotted line indicates that the station received a transmission addressed

to other station.

Request to the slave station1

Res

onse to the master station

Response to the master station

Response to the

master

station

Master

station

Transmit

Receiving

Transmit

Receivin

Transmit

Receivin

Transmit

Receivin

Slave

station 1

Slave

station 2

Slave

station 3

Request to the slave station 2

Request to the slave station 3

Figure 2.37 1 : N Transmitting and receiving sequence

1 2 ... 49 50 51 52 53 54 55 56 57 58 59 ... 66 67

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RTS WM300 Especificaciones Pagina 54

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