Elgas DATCOM, Operating Instructions Manual

Page: 158 / 228

10
Communication with the Device
156
Fig. 76 Principle of connection with PC and external modem via module B-RS
10.3.1 Connecting an external modem
An external modem with RS232 communication interface can be connected to the device.
For the ELCOR
, the external modem is connected either to the terminals of the RS232
communication interface on the I/O board or to the S4-COM0 module. In this case, the S4-COM0
module is installed in the device in a position where the M2G or M4G internal modem is normally
fitted.
For the ELCOR plus and ELCOR plus indexer
, the external modem can be connected either to
the S1-COM1 module, which must be located in the SLOT1 position, or to the S4-COM0 module,
which must be installed in the SLOT 4 position.
Note: If S4-COM0 (SLOT 4) is used, the internal modem in SLOT 5 cannot be used.
In any case, the external modem must be connected to the device via an intrinsically safe barrier
(module B-RS, or MTL5051).
If the connected modem allows it, you can use the service SW [42], [43] to set the parameters of
the external modem communication similarly to the internal modem (see par. 0).
10.4 Encrypting Data when Communicating with the Master
System
This optional feature is implemented in the ELGAS version 2 and CTR protocols. For this
purpose, the device contains cryptographic keys. Symmetric AES encryption with a key length of
128 bits is used. In addition, the packet of transmitted data includes the type of encryption key
and the control signature. Thanks to this signature, the authenticity of the key can be confirmed,
and consequently, the use of the decrypted data permitted. In case of incorrect decryption, the
counterpart is informed by means of a standard error response. Modifying keys is only possible
with highest security level. The keys from an unencrypted packet cannot be accepted.
The implemented protocols include the option to block the device response if an unencrypted
packet has been queried. In the case of such a query, the device responds with a standard error