Technical data

Computing Unit Expansions
4-32
SIMATIC Panel PC 670 Computing Unit Equipment Manual
Edition 12/01
4.11.2 Point-to-Point Connection
Point-to-point connection
This section describes the options for connecting your computing unit to a
programming unit or a programmable controller in a point-to-point connection.
A point-to-point connection is possible by connecting the computing unit to a
programming unit or a programmable controller by means of:
S a V.24 connection
S a TTY connection
You will find detailed notes in section 6.12.
Configuring notes for interfaces with current loop (TTY, 20 mA)
Different criteria have to be taken into account for reliable operation of a
connection. The maximum data transfer rate (baud rate) depends on the required
distance, the type of cable, the pin assignment of the interface and external
interference.
Rules
Observe the following generally applicable rules to reduce interference:
S The shielded cable used must have a low line resistance (< 130 W/km) and a
low capacitance (< 90 pF/m). Twisted-pair cables are less susceptible to
inductive interference. A low line resistance result in reduced voltage
excursions and shorter charge reversal times; the line resistance decreases
with increasing conductor cross-section for the same length of cable.
S The shorter the data transmission link, the higher the maximum possible
transfer rate.
S If there is an active transmitter 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.
S Signal lines and power lines must not be 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).
S The active TTY interface with a 12 V open-circuit voltage has been tested on a
1000 m long cable at a transmission rate of 9600 bps in an environment with
normal levels of noise (field strength < 3 V/m). If a LiYCY 5 x 1x 0.14 shielded
cable is used, reliable transmission is possible over a distance of up to 1000 m.
The AS511 driver was used for testing (only one transmitter at a time).