Alstom GEM80-400 Series, Техническое руководство

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4. Communications GEM80-400
Page 4-6 ALSPA GEM 80-400 SERIES CONTROLLERS TECHNICAL MANUAL Issue 3 04/99
Figure 4.5 - Point-to-Point Serial Communications Link Between Two GEM 80-400
Controllers, RS232
4.3.2. Multi-drop Serial Link
A multi-drop serial link between controllers may be implemented using RS485.
Figure 4.6 shows a multi-drop serial link in which 4 controllers can interchange
data; the control port of GEM
80-400 Controllers can communicate with up to 8
tributary ports (or 15 tributary ports if in user control mode with flexible data
tables). The serial communication port of one controller is set up as a control
port and the others are set up as tributary ports. The control port communicates
with each tributary on a cyclic basis. Direct communication between tributaries
is not possible, though data can be exchanged between tributaries via the
control port provided that the facility exists in the user program of the controller
having the control port. Figure 4.7 shows an example of a typical multi-drop link.
Up to 128 input and output words of data can be exchanged at any one time
and the serial link can be operated in either free-running mode or user-control
mode depending on data set in the P-tables. There is a maximum limit of 512
input and output words to/from all controllers at the control port end. The data
that must be written into the P-table and where data arrives and is transmitted
from is detailed in the following sections, 'Operation as an ESP Tributary Port' and
'Operation as an ESP Control Port', later in this chapter.
TRIBUTARY
PORT
(Set up by Data
in Controller 2
P - Tables )
Tx
PORT 1 Rx
Connector 0V
CONTROL
PORT
( Set up by Data
in Controller 1
P - Tables )
Rx
Tx PORT 1
0V Connector
RS232
50 Feet Maximum Distance
3 2
2
3
5
5