Phone Line Connection; Two And Four Wire Operation; Anti-Streaming - Siemens m50 Series User Manual

3.4.3 NEMA Port 3 Internal Frequency Shift Keying (FSK) Modem

3.4.3.1 Phone Line Connection

Signals are provided on this connector compliant with the NEMA TS-2 Port 3
standard, used for communications via twisted pair to other modem devices, such
as an On-Street Master, typically communicating via ECOM or NTCIP protocol. The
internal FSK modem port is a 9-pin "D" connector conforming to the NEMA PORT 3
communications standard.
receiving on one phone line) and 4-wire (transmitting and receiving on separate
phone lines). FSK means simply that the data binary "ones" and "zeros" are
conveyed over the phone line as two tones, similar to pressing two different
buttons on a touch-tone telephone. The standard modem transmits at 1200 bps,
using 1200 Hz and 2200 Hz as the two transmitting tones. The pin connections of
Port 3 are as follows:
Pin 1 Transmit 1
Pin 2 Transmit 2
Pin 3 Reserved (do not use)
Pin 4 Receive 1
Pin 5 Receive 2
Pin 6 Earth Ground (Equipment Ground)
Pin 7 Reserved (do not use)
Pin 8 Reserved (do not use)
Pin 9 Earth Ground (Equipment Ground)

3.4.3.2 Two and Four Wire Operation

If the internal modem is 2-wire, the single twisted pair phone line is attached to
pins 1 and 2. If the internal modem is 4-wire, the transmitting twisted pair phone
line is attached to pins 1 and 2, while the receiving twisted pair phone line is
attached to pins 4 and 5. Note that these connections also appear on the D Option.
The internal modem is factory programmed for 2-wire operation. The modem may
be changed to 4-wire operation by cutting a programming strap.

3.4.3.3 Anti-Streaming

The internal modem has an anti-streaming option that will turn the modem
transmitter OFF if the EPAC constantly transmits for 7 seconds. This feature is
useful in case the EPAC is damaged and stuck in the transmit mode. Without anti-
streaming, the replies from all other controllers on the line are blocked by the stuck
transmitter. Worse, each modem must be disconnected, one by one, to find the
stuck transmitter. With anti-streaming enabled, the stuck transmitter automatically
turns OFF after 7 seconds, and can be identified by no response from that
controller. Anti-streaming should be disabled on 4-wire master or central modems
that must transmit continuously. Anti-streaming is factory programmed disabled,
and can be enabled by cutting a programming strap.
AUGUST 2005
EPAC300-M50 SERIES USER'S MANUAL
This port supports both 2-wire (transmitting and
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