The CM336 Leased Line Modem

The CM336 was designed out of a need for a product which would transmit and receive data reliably over long distances and which would re-start automatically in the event of power failure or a failure in the line. This product, although still available, is superseded by the CMC56 which is described below.

The CM336 used the Rockwell RC288 Digital Signal Processor (DSP) as is found in many modern modems for use with PCs. This DSP requires a set of commands in order for it to operate and this is normally provided by the PC itself via the AT command protocol. This is far too complicated for a modem link over a leased line. In many cases, commercial modems are only supplied with dial-up commands so could not be used over a leased line in any case.

New Modem Products

The CM336 above is designed for leased lines only but, with the relaxation of rules governing connection to the PSTN and a Europe-wide compliance standard (with local variants), we have now developed a PSTN version which enables remote dialling for data collection, for example. A typical application would have the phone number of a central monitoring location stored in flash memory so that the CMC56 could call up in the event of an alarm, for example. Similarly, the central location would be able to dial up the CMC56 at regular intervals in order to 'poll' it for information.

The new modem products are very much smaller than the CM336 illustrated above, partly because we made the original CM336 all singing-dancing with several types of interface and partly because the components are now much smaller and consume less power.

The photo shows the CMC56 in its wall-mounted steel box. Click on the photo to view CMC56.pdf

The PSTN version of the CMC56 uses the new Conexant RC56 modem data-pump in an all-3volt circuit driven by a Motorola MC68HC908JL3 processor. The interface to the telephone line is via a Mitel transformerless thick film circuit which ensures a flying start when approval is required.

Note: this product is no longer availalable - page published here for archive purposes