Vega VEGACOM 557 Siemens 3964 and 3964 R procedure with Bedienungsanleitung PDF herunterladen (Seite 33)

VEGACOM 557 Siemens 33

Supplement

6 Supplement

6.1 Short description of the stand-

ard interfaces RS 232, RS 422

and RS 485

The standard interfaces RS 232, RS 422, RS

485 used in VEGACOM 557 depending on

the version, transmit the data serially and

asynchronously in bit form. Thereby the con-

ditions "0" and "1" are transmitted by defined

voltage levels. Usually, the transition level

corresponds to a logic "1". The respective

levels are specified in the following informa-

tion to the individual interfaces.

Standard data transmission

0 00000 0

1111

0

1

Data bits

Transition level

Stop bits

MSB

LSB

Start bit

Transition level

MSB = most significant bit

LSB = least significant bit

Number of data bits = 8

A parity bit can follow the last data bit which

is used for detection of transmission errors.

The parity bit ensures that with

- EVEN parity always an even number of bits

- ODD parity always an odd number of bits

is transmitted.

A so-called handshake can be used to re-

lease or interrupt the data transmission.

Hardware handshake:

The receiver controls via its handshake out-

puts DTR or DSR the handshake inputs CTS

or DSR of the emitter.

Software handshake:

The receiver emits special characters to the

transmitter and with this, controls the data

transfer.

Although there is no standard for the inter-

faces RS 232, RS 422 and RS 485, they can

be taken as a standard because they are

handled as industrial standard.

The interface RS 232 transmits the individual

bits of a character as sequence of defined

voltage levels via one cable.

Therefore:

- a voltage level of -15 V … -3 V corre-

sponds to a logic "1"

- a voltage level of +3 V … +15 V to a logic

"0".

Both levels are related to a common signal

ground (GND). The permissible, ohmic load

must be more than 3 kOhm, the permissible

capacitive load can be max. 2500 pF.

Main characters of a RS 232 interface are

- reduced cable length (max. 15 m to

9600 baud)

- low data rates (max. 19200 baud)

- only point-to-point connection

For industrial applications, the provided

handshake signals are not necessary. For

this, the handshake inputs are just connected

to the handshake outputs of the same instru-

ment (release level).

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