Black Box ME728A 150-0528-103 8-Port Async Line Driver Multiplexer DB25 RS-232

Black Box ME728A 150-0528-103 8-Port Async Line Driver Multiplexer DB25 RS-232

The Black Box ME728A is an 8-port asynchronous line driver multiplexer designed to extend and concentrate multiple RS-232 serial data streams over a shared link. Identified on the unit as the LD-478, it multiplexes up to eight asynchronous serial channels — each on a DB25 interface — onto a single transmission path, making it well-suited for connecting clusters of terminals, printers, or other serial devices to a host system or data switch across longer distances than standard RS-232 allows. The unit houses its logic and power supply in a compact black desktop enclosure and is configurable via internal DIP switch banks.

Specifications & What's Included

• Manufacturer: Black Box Corporation
• Model: ME728A (also labeled LD-478 on front panel)
• Part Number: 150-0528-103
• Number of Channels: 8 asynchronous serial ports
• Connector Type: DB25 (25-pin) per channel
• Signal Standard: RS-232 asynchronous serial
• Input Voltage: 115V AC
• Current Draw: 1.2A
• Frequency: 50/60 Hz
• Form Factor: Desktop enclosure
• Country of Manufacture: Puerto Rico – USA
• Certifications: UL listed, CSA listed
• FCC Compliance: Part 15 Class A
• Internal DIP switches: Switch Selection (standalone / Micro500 mode, distance select, dynamic/RCVD control), RTS/DTR Select per channel, RCVD Control per channel, loopback per channel
• Channel terminals visible on internal connector row: T1, R1, T2, R2, T3, R3, T4, R4, T5, R5, T6, R6, T7, R7, T8, R8, TX, RX, EM, SL, DLB
• Internal power supply module housed in vented metal sub-chassis
• Attached AC power cord included

Applications

Asynchronous line driver multiplexers like the Black Box ME728A were standard equipment in data centers, industrial control rooms, and enterprise computing environments from the late 1980s through the 1990s, where large numbers of RS-232 serial devices — dumb terminals, point-of-sale terminals, serial printers, barcode readers, and similar peripherals — needed to share access to a minicomputer, mainframe, or communications server. By multiplexing multiple async channels onto a single wire run, a device like this allowed a single cable infrastructure to serve an entire cluster of serial devices, reducing wiring costs and simplifying the physical plant. The Micro500 compatibility mode visible in the DIP switch labeling indicates integration with Black Box's own Micro500 multiplexer/concentrator product line. These devices are still sought after in legacy industrial and institutional environments running older serial-based control or data-collection systems that have not yet migrated to modern networking, and by integrators maintaining compatibility with installed RS-232 serial equipment.