Murton System Technologies have
achieved an exceptional signal to noise ratio in the new OEM DSP-CODEC modem
designed for telemetry applications, now available for general use.
“For most point-to-point
telemetry applications, modems are used in a ‘polling’ environment or in a
master-slave configuration. The master polls each device or node connected
to it periodically,” added Brent Maurer Murton System
“Modern modems, the ones
designed for connection to the Internet for example, require a considerable
amount of preamble time to negotiate various communication parameters when they
connect. Internet modems embark on a complex set of negotiations at the
start up to determine the best baud rate, error correction scheme and
communications protocol. This takes several seconds to accomplish,”
In a telemetry application, the
host needs an immediate response from any device it polls and no time can be
spent on negotiating a set of communication standards. “With this in mind, we
developed the modem,” said Maurer.
At the hardware level the modem
consists of 60MHz internal DSP (digital signal processor) connected to an
industry standard CD quality stereo CODEC (coder/decoder). The DSP and
CODEC connect to one another via a high-speed industry standard serial bus.
On the user interface side of
the modem both ‘left’ and ‘right’ signals are available. Both
CODEC channels are made available allowing the end user applications to
implement a number of options such as main or standby configuration, data
routing and dual channel modem configuration.
Signals can be sampled at 44kHz
making the CODEC ideal for medium to high-speed FSK applications.
The host side connection is
achieved by means of a standard MOTEL (Motorola/Intel) parallel interface.
“As most off-the-shelf modems have a serial interface for hooking up to the
control equipment, it was decided to use a parallel interface,” comments
This has several advantages for
embedded applications. Firstly, the need for a UART (universal
asynchronous receiver transmitter) is eliminated. Secondly, the processor
overhead requirement and transfer speed between host and DSP, for most embedded
controller types, is substantially reduced since the transfer of data between
controller and modem is done on a byte wide basis. Thirdly, the design
allows for a ‘host download’ connection to the modem. What this means,
is that at start up, the host controller downloads the firmware code into the
Only the firmware required by
the application is downloaded into the DSP memory at run time.
The original firmware currently
implements FSK communications. The firmware is based on the standard sine wave
generation techniques used with CODEC’s but uses a unique demodulation process
of statistically comparing the incoming signal with both the possible FSK
signals representing 1 and 0.
The modem is currently
available as an OEM card without firmware and customized firmware is available