Technical data

SIMATIC Box PC 620 Expansions
5-30
SIMATIC Box PC 620 Manual
C79000-G7076-C639-02
5.11.2 Point To Point Connection
Point-To-Point Connection
In this chapter, the possibilities of linking your device to a programming unit or a
programmable controller in a point-to-point connection are described.
You can establish a point-to-point connection by connecting the SIMATIC Box PC
620 to another programming device or a programmable logic controller using
 A V.24 connection
 A TTY connection
Configuring Interfaces with Line Current (TTY, 20 mA)
For reliable internetworking operation, various criteria must be taken into account.
The attainable data transfer rate (baud rate) is thereby dependant on the desired
distance, the selected cable type, the selected interface RC circuit and the
disturbing influences which are present.
Rules
You can reduce interference by choosing the right transmission cable and
connecting it properly, and by observing the following guidelines:
 Use a shielded cable with a low line resistance (130  / km) (about 40 kft)
and low capacitance (< 90 pF/m) (about 27 pF/ft). Twisted-pair cables are less
susceptible to noise and interference. A low line resistance results in reduced
voltage excursions and shorter charge reversal times. The line resistance
decreases with increasing conductor cross-section for the same length of cable.
 The shorter the transmission link, the higher the maximum possible data
transfer rate.
 If there is an active sender and an active receiver at the same end of the
transmission link, the sequence of access priority to the transmission circuit
must be taken into account in order to achieve the longest possible
transmission link.
 Signal lines and power lines must not run together. Signal lines must be
installed as far away as possible from sources of strong interference (for
example, 400 V 3-phase power cables).
 The active TTY interface with a 12 V no-load voltage has been tested on a 100
m (1100 ft) long cable at a transmission rate of 9600 bps in an environment with
normal levels of noise (field strength < 3 V/m or 1 V/ft). If a shielded LiYCY 5 x
1 x 0.14 shielded cable is used, reliable transmission is possible over a distance
of up to 100 m (1100 ft). The AS511 protocol (only one transmitter at a time)
was used for testing.
Note
The interference field of the source of interference is reduced by the square of the
distance.