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2014

年

6

月< /p>

Understanding the Basics of S7-200 Network Communications

Selecting the Communication Interface for Your Network

The S7-200 is designed to solve your communications and networking needs by

supporting

not

only

the

simplest

of

networks

but

also

supporting

more

complex

networks. The S7-200 also provides tools that allow you to communicate with other

devices,

such

as

printers

and

weigh

scales

which

use

their

owncommunications

protocols.

The

S7-200

supports

many

different

types

of

communication

networks.

The

selection of a network isperformed within the Set PG/PC Interface property dialog. A

selected

network

is

referred

to

as

an

Interface.

The

different

types

of

interfaces

available to access these communication networks are:

1. PPI Multi-Master cables

2. CP communication cards

3. Ethernet communication cards

To select the communication interface for STEP 7--Micro/WIN, you perform the

following steps. See Figure 7-1.

1. Double-click the icon in the Communications Setup window.

2. Select the interface parameter fo

1

2

Figure 7-1 STEP 7--Micro/WINCommunications Interface

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PPI Multi-Master Cables

The S7-200 supports communication through two different types of PPI Multi-Master

cables. These cable types permit communication through either an RS-232 or a USB

interface.

As

shown

in

Figure

7-2,

selecting

the

PPI

Multi- Master

cable

type

is

simple.

You

perform the following steps:

1. Click the Properties button on the Set PG/PC Interface property page.

2. Click the Local Connection tab on the Properties page.

3. Select the USB or the desired COM port

Figure 7-2 PPI Multi-Master Cable Selection

1

2

3

Tip

Please note that only one USB cable can be used at a time.

Tip

Examples

in

this

manual

use

the

RS-232/PPI

Multi-Master

cable.

The

RS-232/PPI

Multi-Master

cable

replaces

the

previous

PC/PPI

cable.

A

USB/PPI

Multi-Master cable is also available. Refer to Appendix E for order numbers.

Using Master and Slave Devices on a PROFIBUS Network

The S7-200 supports a master-slave network and can function as either a master

or a slave in a PROFIBUS network, while STEP 7--Micro/WIN is always a master.

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Masters

A device that is a master on a network can initiate a request to another device on

the network. A master can also respond to requests from other masters on the network.

Typical

master

devices

include

STEP

7--Micro/WIN,

human-machine

interface

devices such as a TD 200, and S7-300 or S7-400 PLCs. The S7-200 functions as a

master

when

it

is

requesting

information

from

another

S7-200

(peer-to-peer

communications).

Tip

A TP070 will not work on a network with another master device.

Slaves

A device that is configured as a slave can only respond to requests from a master

device; a slave never initiates a request. For most networks, the S7-200 functions as a

slave.

As

a

slave

device,

the

S7-200

responds

to

requests

from

a

network

master

device, such as an operator panel or STEP 7--Micro/WIN.

Setting the Baud Rate and Network Address

The speed that data is transmitted across the network is the baud rate, which is

typically measured in units of kilobaud (kbaud) or megabaud (Mbaud). The baud rate

measures

how

much

data

can

be

transmitted

within

a

given

amount

of

time.

For

example, a baud rate of 19.2 kbaud describes a transmission rate of 19,200 bits

per

second.

Every

device

that

communicates

over

a

given

network

must

be

configured

to

transmit data at the same baud rate. Therefore, the fastest baud rate for the network is

determined by the slowest device connected to the 7-1 lists the baud

rates supported by the S7-200.

Table 7-1 Baud Rates Supported by the S7-200

Network

Standard Network

Baud Rate

9.6 kbaud to 187.5 kbaud

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Using an EM 277

Freeport Mode

9.6 kbaud to 12 Mbaud

1200 baud to 115.2 kbaud

The network address is a unique number that you assign to each device on the

network.

The

unique

network

address

ensures

that

the

data

is

transferred

to

or

retrieved from the correct device. The S7-200 supports network addresses from 0 to

126. For an S7-200 with two ports, each port has a network address. Table 7-2 lists

the default (factory) settings for the S7-200 devices.

Table 7-2 Default Addresses for S7-200 Devices

S7-200 Device

STEP 7-- Micro/WIN

HMI (TD 200, TP, or OP)

S7-200 CPU

Default Address

0

1

2

Setting

the

Baud

Rate

and

Network

Address

for

STEP

7--Micro/WIN

You must configure the baud rate and network address for STEP 7--Micro/WIN.

The baud rate must be the same as the other devices on the network, and the network

address must be unique.

Typically, you do not change the network address (0) for STEP 7-- Micro/WIN.

If

your

network

includes

another

programming

package,

you

might

need

to

change

the network address for STEP 7--Micro/WIN.

As shown in Figure 7-3, configuring the baud rate and network address for STEP

7--Micro/WIN is simple. After you click the Communications icon in the Navigation

bar, you perform the following steps:

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Figure 7-3 Configuring STEP 7-- Micro/WIN

Figure 7-3 Configuring STEP 7--Micro/WIN

1

2

3

4

1. Double-click the icon in the Communications Setup window.

2. Click the Properties button on the Set PG/PC Interface dialog box.

3. Select the network address for STEP 7--Micro/WIN.

4. Select the baud rate for STEP 7--Micro/WIN.

Setting the Baud Rate and Network Address for the S7-200

You must also configure the baud rate and network address for the S7-200. The

system block of the S7-200 stores the baud rate and network address. After you select

the parameters for the S7-200, you must download the system block to the S7-200.

The default baud rate for each S7-200 port is 9.6 kbaud, and the default network

address is 2.

As

shown

in

Figure

7-4,

use

STEP

7--Micro/WIN

to

set

the

baud

rate

and

network

address

for

the

S7-200.

After

you

select

the

System

Block

icon

in

the

Navigation bar or select the View > Component > System Block menu command, you

perform the following steps:

1. Select the network address for the S7-200.

2. Select the baud rate for the S7-200.

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3. Download the system block to the S7-200.

1

2

Figure 7-4 Configuring the S7-200 CPU

Tip

Selection

of

all

baud

rate

options

is

permitted.

STEP

7--Micro/WIN

validates

this

selection

during

the

download

of

the

System

Block.

Baud

rate

selections

that

would

prevent

STEP

7--Micro/WIN

from

communicating

with

the

S7-200

are

prevented from being downloaded.

Setting the Remote Address

Before you can download the updated settings to the S7-200, you must set both

the communications

(COM) port of STEP

7--Micro/WIN (local) and the address

of

the S7-200 (remote) to match the current setting of the remote S7-200. See Figure 7-5.

After

you

download

the

updated

settings,

you

may

need

to

reconfigure

the

PG/PC

Interface

baud

rate

setting

(if

different

from

the

setting

used

when

downloading to the remote S7-200). Refer to Figure 7-3 to configure the baud rate.

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Figure 7-5 Configuring STEP 7-- Micro/WIN

Searching for the S7-200 CPUs on a Network

You

can

search

for

and

identify

the

S7-200

CPUs

that

are

attached

to

your

network. You can also search the network at a specific baud rate or at all baud rates

when looking for S7-200s.

Only PPI Multi-Master cables permit searching of all baud rates. This feature is

not available if communicating through a CP card. The search starts at the baud rate

that is currently selected.

1.

Open

the

Communications

dialog

box

and

double- click

the

Refresh

icon

to

start the search.

2. To search all baud rates, select the Search All Baud Rates check box. 2.

Selecting the Communications Protocol for Your Network

The

following

information

is

an

overview

of

the

protocols

supported

by

the

S7-200 CPUs.

1. Point-to-Point Interface (PPI)

2. Multi-Point Interface (MPI)

3. PROFIBUS

Figure 7-6 Searching for CPUs on a Network

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Based

on

the

Open

System

Interconnection

(OSI)

seven-layer

model

of

communications

architecture,

these

protocols

are

implemented

on

a

token

ring

network

which

conforms

to

the

PROFIBUS

standard

as

defined

in

the

European

Standard

EN

50170.

These

protocols

are

asynchronous,

character- based

protocols

with

one

start

bit,

eight

data

bits,

even

parity,

and

one

stop

bit.

Communications

frames depend upon special start and stop

characters, source and destination station

addresses, frame length, and a checksum for data integrity. The protocols can run on a

network simultaneously without interfering with each other, as long as the baud rate is

the same for each protocol.

Ethernet is also available for the S7-200 CPU with expansion modules CP243--1

and CP243--1 IT.

PPI Protocol

PPI

is

a

master-slave

protocol:

the

master

devices

send

requests

to

the

slave

devices, and the slave devices respond. See Figure 7-7. Slave devices do not initiate

messages, but wait until a master sends them a request or polls them for a response.

Masters

communicate

to

slaves

by

means

of

a

shared

connection

which

is

managed

by

the

PPI

protocol.

PPI

does

not

limit

the

number

of

masters

that

can

communicate with any one slave; however, you cannot install more than 32 masters

on the network.

Figure 7-7 PPI Network

S7-200

CPUs

can

act

as

master

devices

while

they

are

in

RUN

mode,

if

you

enable

PPI

master

mode

in

the

user

program.

(See

the

description

of

SMB30

in

Appendix D.) After enabling PPI master mode, you can use the Network Read or the

Network Write instructions to read from or write to other S7-200s.

While the S7-200 is acting as a PPI master, it still responds as a slave to requests

from other masters.

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