NBEK Controller As 1200 Baud Modem

The Narrow band Evaluation Kit (NBEK) IC can be used as 1200baud half-duplex serial modem suitable for narrow band receivers, transmitters and transceivers (or any RF modules with >5kbps data rate). It takes care of preamble, synchronisation, bit balancing and error checking and enables a transparent radio data link to be established between radio devices. This is a half duplex unit, so collisions between transmitted and received packets must be dealt with by the user. Provided no two devices attempt to transmit simultaneously no further restrictions on data transmission need be made, as all transmit timing, valid data identification and data stream buffering is conducted by the unit. Synchronisation and framing words in the packet prevent the receiver outputting garbage in the absence of wanted RF signal or presence of interference. Supports 1200 baud asynchronous data: 1 start bit, 8 data bits, 1 stop bit.

With typical microcontrollers and UARTs, direct connection is usable as shown on figures 2 & 3. To connect to a true RS232 device, inverting level shifters must be used (MAX232 type are ideal, but simple NPN/PNP transistor switches often suffice as used in the application circuits figures 4 & 5).


  • Operating voltage (temperature): 5V for standard version (-40°C to +85°C)
  • Maximum usage of the range capability of an RF module
  • Adequate preamble to settle data slicer in the receiver
  • Extra wake up preamble to allow for transmitter power up time requirements
  • Differential Manchester encoding of address, data and checksum
  • Synchronisation codes and checksum to reduce false triggering on noise
  • Suitable to be used with Narrow Band FM radio modules
  • Serial modem baud rate at 1200bps (half-duplex)
  • Addressable point-to-point


  • PDAs, organisers & laptops
  • Handheld / portable terminals
  • EPOS equipment, barcode scanners
  • In-building environmental monitoring and control
  • Remote data acquisition system, data logging
  • Fleet management, vehicle data acquisition