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If you have a special application, we may already have a solution for you.
Give Ron a Call at 513-874-4796 or 513-638-0228 for additional information.
QASC24: Quad RS232 to RS485 2 Wire Half Duplex Non-isolated Converters


QASC24 with Box

QASC24 Label

"Let me spin a very large
RS485 network for you!"


Product Features:

  • This quad channel(cell) auto transmit unit features bi-directional serial conversion from RS232 to RS485 in 2 wire half-duplex communications mode.

  • Each of the 4 cells are independent and functionally identical to the ASC24. This unit can potentially replace up to 4 single cell converters, with a savings in cost and space.

  • Optimized for non-isolated office/indoor point to point or multi-drop systems. Each RS485 transceivers can drive 32 standard loads at 4000 ft, at data rates up to 115.2 Kbps.

  • Transparent to all asynchronous data, with any combination of data, parity, and stop bits. No need to set switches or jumpers.

  • Fast auto turn-around, from transmit to receive mode, requires no software delays and eliminates timing problems and data collisions. A special jumper(JS) can further shorten the turn-around time to accommodate fast responding target devices. We pioneered and perfected this leading edge technology long before our competition.

  • Each RS485 transceiver is protected with 22 Ohm series resistors, and built in ESD tolerance.

  • Jumpers allow the RS485 termination and bias resistors to be user configured. Jumper JM will place the unit in Loop-Back mode for self test. 

  • Board and edge mounted LEDs display the regulated power. Each cell has its own edge mounted LEDs displaying data activity. 

  • A polarity protected switching power regulator accepts supply voltages from 9 to 35VDC, at 2 Watts max. 

  • Broad environmental range. Temperature: -40C to +85C(-40F to +185F). Humidity: 10 to 90% RH(non-condensing)

  • Four(4) easy mount through hole standoffs, which accept #6 hardware, are provided on the circuit board.

  • User connections are 3 pin screw terminal strips for the RS232 and RS485(each cell), and a 2 pin screw terminal strip and 2.1 mm barrel connector(common power).

  • Accessories available are a 12VDC Switching Power Supply(Wall Wart), and an enclosure.

  • Conformal Coating, and connectors, are factory options. Contact us for options help.

  • R E Smith also provides several similar single channel converters with different connectors and LEDs. Check out the ASC24, ASC24R, ASC24W, ASC24T,  and ASC24TS family.

  • We also have a new series of Converters and Repeaters that extend the RS485 communications distance far beyond conventional limits. In some configurations, up to 5 miles/38.4Kbps.

  • R E Smith Inc makes a wide variety of isolated converters that address the electrical noise problems that contribute to unreliable communications, and product failure.  If what you see here is not exactly what you need, don't hesitate in calling us at 513-874-4796.

  • WARNING: Do NOT connect this device to a telephone system under any circumstances. Damage could result to the circuit board and/or your telephone system.

About R E Smith, Inc.

R E Smith, Inc. engineers and manufactures a comprehensive line of isolated and non-isolated converters, repeaters, multiport repeater hubs, fiber optic based products, and I/O boards. All our products are designed, built, tested, and shipped from our facility in the Greater Cincinnati Ohio area. We ship small quantities of most products from stock the same day, and larger quantities in a few business days.

We listen to you. We are customer driven. Many of our products were developed and improved due to suggestions and feedback from our word-wide customer base. They are being used at the South Pole, at the bottom of the sea, at the edge of space, and everywhere in between. Typical uses are very large networks, monitor and control of elevators, machinery, lighting, security, fire and alarm, access, cameras, military ground support, and much more. We provide free support, no-argument warranty repairs, and recommendations for your application. Challenge us with your communications problem. We may already have the solution. If your system keeps failing, or is unreliable, we have isolated, doubly isolated, noise resistant, cost effective, and proven solutions for difficult environments.

Related Files:

pdf icon QASC24ABrevA.pdf Converter schematic/physical Rev A
pdf icon QASC24CDrevA.pdf Converter schematic/physical Rev A


RS232: 3-wire screw terminal strip(TX, RX, Common)(each cell)
RS485: 3-wire screw terminal strip(RxTx+, RxTx-, Common)(each cell)
Power: 2-wire screw terminal strip and a 2.1mm center positive "Barrel" connector (9-35VDC)
LEDs Board and edge mounted regulated power, and Data activity(each cell)
Bias: 620 Ohm pull-up and pull-down (jumper selectable)(each cell)
Termination: 120 Ohm (jumper selectable)(each cell)
Protection: 22 Ohm series resistors, Sipex SP485 EEP/REP Driver with built in ESD tolerance(each cell)


Distance: Up to 4000 ft. (1220 meters)
Operation: RS232 to 2-wire half-duplex RS485
Format: Asynchronous data with any combination of data, parity, and stop bits
Speed: Up to 115.2Kbps
Environmental: -40C to +85C ambient, 10-90% RH non-condensing
Supply Power: 9-35VDC at 0.5 Watts typical + external loads
Size: 4" X 3.75" X 0.9" (nominal)(PC Board only)
Mounting: 4-Holes at 2.25" X 3" (built-in standoffs for #6 hardware)

Options and Ordering Information:

QASC24W: $159.00 ea. (Circuit board only)
Enclosure: $10.00 ea. (Medium)
Cable: No cable(s) available. (Direct wire to screw terminal strips)
Supply: $8.50 ea. (12VDC/0.5A switching regulated wall power supply). Meets California, and most world wide safety and efficiency standards.

This is the QASC24 unit showing the complete order number

QASC24 with all options (Enclosure and PS): Order Number: QASC24-BSPS @ $177.50 ea. (Qty. 1-9)

Need a different configuration or more information? Give Ron a Call at 513-874-4796 or 513-638-0228(Cell)


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