USER MANUAL – Z-PASS1/Z-PASS2
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The Remote Serial COM functionality lets to a PC Application, which transmits data only over a serial line, to
communicate with a remote serial device, using Ethernet/Internet; in other word, through a Z-PASS, a PC
and a serial device, placed in sites distant from each other, can communicate as they are directly
connected.
In this mode, data sent over the LAN or WAN network, are received by the Z-PASS and sent to the serial
port; response packets follow the reverse path.
RFC 2217 defines some features that let the PC remotely set the properties (baud rate, data bits, stop bits
and parity) of the Z-PASS serial port; so, when the Remote Serial COM operating mode is selected for one
port, the port is reconfigured regardless of the previous settings and the values configured by means of the
“Serial Ports” web page are overwritten.
To allow the Remote Serial COM work, an utility called “Seneca Ethernet to Serial Connection” shall be
installed on the PC; this is explained in details in 11.1.1 paragraph.
The TCP connection can be established over a VPN tunnel, as shown in the figures at the beginning of the
paragraph.
Once the connection is established, a program using the remote serial COM port will transmit data to the Z-
PASS serial port; for example, Modbus RTU requests sent by a Modbus Master program will reach Modbus
slave devices connected to the COM2 RS485 bus.
A particular notice shall be given about the “Data Packing Interval” parameter, that can be set when
Remote Serial COM operating mode is selected: this parameter lets you define the time interval, in
milliseconds, used by Z-PASS as a criterion to pack the data bytes received from the serial port before
sending them to the network; in other words, when Z-PASS does not receive any more bytes from the serial
port for the given time interval, it packs the received bytes and send them over the established TCP
connection; the optimal value to be set for this parameter depends on the protocol that is transparently
routed from the TCP/IP network to the serial line and vice versa.
WARNING!
In the Remote Serial COM operating mode, just one connection is accepted for a given serial port.
