Black Box ME1791A-F User manual

JULY 2003
ME1791A-F ME1794A-F
CUSTOMER
SUPPORT
INFORMATION
Order toll-free in the U.S.: Call 877-877-BBOX (outside U.S. call 724-746-5500)
FREE technical support 24 hours a day, 7 days a week: Call 724-746-5500 or fax [phone]
Mailing address: Black Box Corporation, 1000 Park Drive, Lawrence, PA 15055-1018
Web site: www.blackbox.com • E-mail: [email protected]
Ultra-Miniature
Asynchronous Short
Range Modems

Description 1
ME1791A-F, ME1794A-F
1. Features
Ultra-miniature asynchronous short range modems:
• Ultra-miniature modems using hybrid technology
• Asynchronous transmission up to 19.2 kbps
• Transmission range up to 21 km (13 miles)
• No AC power required
• 9-pin RS-232/V.24 connector
• Can be used with both STP and UTP
• Compact, lightweight, easy to install.
Versions
The following versions of the modem are available:
• ME1791A-F – modem with female DCE connector and terminal block line
connector
• ME1794A-F – modem with female DCE connector and RJ-45 line connector.
Application
Async
Computer
Asynchronous
Ter mi na l
4-wire
ME1791A-F,
ME1794A-F
ME1791A-F,
ME1794A-F
Figure 1. Typical Application
2. Description
ME1791A-F and ME1794A-F, ultra-miniature asynchronous short range modems,
are used for local data distribution, connecting full duplex asynchronous DTEs to
computers.
The modems ensure integrity of data transmission, using unconditioned 4-wire
dedicated lines at data rates up to 19.2 kbps. It operates over distances up to
21 km (13 miles) depending on wire gauge and data rate (see Table 1).

ME1791A-F, ME1794A-F
2 Description
Table 1. Typical Transmission Ranges
19 AWG 24 AWG 26 AWGData Rate
[kbps] [km] [miles] [km] [miles] [km] [miles]
19.2 14 9 6 4 4 3
9.6 14 9 6 4 5 3
4.8 14 9 7 4 5 3
2.4 16 10 8 5 7 4
1.2 21 13 11 7 8 5
The modems incorporate innovative circuitry design, which enables the units to
operate without connection to the mains supply, by using ultra low power from
the standard RS-232/V.24 data and control signal voltages. The modem operates
fully even if only Transmit Data is connected (i.e. without the DTE sending Request
to Send or Data Terminal Ready signals). Both positive and negative signals are
generated in compliance with RS-232/V.24 standards, regardless of constantly low
or constantly high Transmit Data. Table 2 provides the DCE connector pinout.
Table 2. DCE Connector Pinout
Pin Designation Function
1 DCD Data Carrier Detect (output)
2 RD Receive Data (output)
3 TD Transmit Data (input)
4 DTR Data Terminal Ready (input)
5 GND Ground
6 DSR Data Set Ready (output)
7 RTS Request To Send (input)
8 CTS Clear To Send (output)
9 RI (+V)
The low transmit level minimizes cross-talk onto adjacent circuits within the same
cable. Data is transmitted and received at a balanced impedance, ensuring
excellent immunity to circuit noise.
The line side of the modems offers connection to the RS-232 plug ground.
This may be connected to the shield of the STP wiring to provide end-to-end
ground continuity. Table 3 provides the pinout of the RJ-45 line connector.

ME1791A-F, ME1794A-F
Technical Specifications 3
Table 3. Line Connector Pinout (RJ-45)
Pin Function
1 Not connected
2 Ground
3 RCV-
4 XMT-
5 XMT+
6 RCV+
7 Not connected
8 Not connected
3. Technical Specifications
Line Interface Line Type 4-wire unconditioned dedicated line
(two twisted pairs)
Transmission Mode Asynchronous, full duplex
Transmission Level -6 dBm
Range See Table 1
Connector • ME1791A-F: 4-screw terminal block
• ME1794A-F: RJ-45
DCE Interface Type RS-232/V.24
Data Rate Up to 19.2 kbps
Control Signals DSR (Circuit 107) and DCD (Circuit 109) turn
on immediately after the terminal raises DTR
(Circuit 108.2);
CTS (Circuit 106) turns on immediately after
the DTE raises RTS (Circuit 105)
Connector D-type, 9-pin, female
Power No external power supply is required; the
modems use ultra low power from the
RS-232/V.24 data and control signals
Physical Height 19.8 mm / 0.8 in
Width 31 mm / 1.2 in
Depth 61 mm / 2.4 in
Weight 26g / 0.9 oz
Environment Temperature 0–50°C (32–122°F)
Humidity Up to 90%, non-condensing

ME1791A-F, ME1794A-F
4 Installation
4. Installation
Installation of the modems is simple and straightforward, just follow these steps:
1. Connect the 4-wire dedicated line to the line connector; transmit pair to
‘XMT’ and receive pair to ‘RCV’.
Observe the following pin polarity between the local and remote units:
 Local XMT+ connected to remote RCV+
 Local XMT- connected to remote RCV-
 Local RCV+ connected to remote XMT+
 Local RCV- connected to remote XMT-.
2. Connect the modems directly to the 9-pin connector of the DTE or the
computer and fasten with the two screws – one on each side of the modem
connector.