Data handling modem

The 19600, from Radiometrix, is a 9600 Bps half-duplex serial modem controller, which is suitable for use with wideband receivers, transmitters and transceiver systems.

It takes care of all the preamble, synchronisation, bit balancing procedures, and enables a transparent radio data link to be established between radio devices.

As long as two devices do not attempt to transmit simultaneously, no further restrictions on data transmission need to be made, as all transmit timing, valid data identification and datastream 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 the presence of interference.

For multiple radio systems the unit can be set to one of eight addresses, allowing complex infrastructure to be deployed without performance being compromised. To connect to a true RS232 device, inverting level shifters must be used.

With the incorporation of typical microcontrollers and UARTs into the system, direct connection is possible.

A 32 byte software FIFO is implemented in both transmit and receive sub-routines. At the transmitting end this is used to allow for the transmitter start-up time (about 3 ms), while on receiving end it buffers arriving packets to the constant output data rate.

All timing and data formatting tasks are handled by the internal firmware. The user does not have to worry about keying the transmitter before sending data as the link is entirely transparent.

For transmission across the radio link, data is formatted into packets (each comprising 3 bytes of data and a sync code). If less than 3 bytes are in the transmit end FIFO then a packet is still sent, but idle codes replace the unused bytes.