NBEK Controller As 1200 Baud Modem
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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): 5 V 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

mode select bits Figure 2: package type, 18-Lead Plastic Dual In-line (PDIP - 300mil wide body) Pin description: 2. TXD, RXD, RSRXD, RSTXD and STATUS are 5V CMOS logic level 3. Some Radiometrix transmitters require 3V logic levels on their transit data inputs: a divider (4.7kQ series, 10kQ to ground) on the TXD pin is needed 4. In RX operation, RXD becomes a high impedance 5. After pulling TXE low (active), the coder allows about 50mS for TX to power up and settle 6. RSTXD (7) has no pullup. If the device is only used for receive, then tie this pin to VCC 7. Vcc must be a 5v regulated...

The mode select bits M0-M3 put NBEK IC in to one of 16 operating modes, including modem mode. 1. Mode 12 and 13 require Transceiver 2. In Mode 12, a test packet is transmitted, then the unit switches to Receive mode for 100ms before repeating. 4. In Mode 13, the unit idles in Receive mode. When a valid CTR44 burst is received the unit keys up the Transmitter and re-transmits this CTR44 burst back to sender in Mode 12. Radiometrix Ltd Page 3 1200buad Modem IC

Operating principle of modem This device is a simplex link handling a 1200 baud asynchronous datastream (1 start, 8data, 1stop). Buffering in the transmit end handles TX startup timing requirements, while the presence of sync codes in the transmitted bursts prevents the receiver from outputting garbage in the presence of noise. No error correction or retransmission of lost packets is supported. To operate with proper +/-12V RS232 levels an external buffer (such as a MAX232) will be needed Operation: Serial interface Both transmit and receive modems implement a 32 byte software FIFO. At the...

Application Circuits Figure 2: NBEK IC interfaced to a Transmitter (e.g. TX1) Note: Note 1. Transmit keyed when valid serial data is present at the RSTXD input, so no separate TX control needed 2. OSC1,2 require a 3.58MHz ceramic resonator with internal capacitors like Murata CSTLA3M58G55-B). If a 2 pin resonator or crystal is used, then two 15pF caps are needed: one from OSC1 to 0V; one from OSC2 to 0V RESET VSS NC RSTXD RXD µC UART Figure 3: NBEK IC interfaced to a Receiver (e.g. NRX1)

Figure 4: RF Transmitter (e.g. TX1) + NBEK IC interface for RS232 data transmission Figure 5: RF Receiver (e.g. NRX1) + NBEK IC interface for RS232 data reception Ordering Information: The NBEK controller IC can be ordered separately with equal number of radio modules. NBEK-000-SS - Shrink Small Outline NBEK-000-SO - Small Outline NBEK-000-DIL - Plastic Dual In Package

European Radiocommunications Office (ERO) Peblingehus Nansensgade 19 DK 1366 Copenhagen Tel. +45 33896300 Fax +45 33896330 ero@ero.dk www.ero.dk Copyright notice This product data sheet is the original work and copyrighted property of Radiometrix Ltd. Reproduction in whole or in part must give clear acknowledgement to the copyright owner. Limitation of liability The information furnished by Radiometrix Ltd is believed to be accurate and reliable. Radiometrix Ltd reserves the right to make changes or improvements in the design, specification or manufacture of its subassembly products...