The FX614/MX614 is a low power CMOS integrated circuit for the reception or transmission of asynchronous 1200bps data, and is suitable for use in Bell 202 type systems. It is also capable of generating the 5bps or 150bps back channel.
The device incorporates an optional Tx and Rx data retiming function that removes the need for a UART in the associated µC when operating at 1200bps.
An optional line equaliser in incorporated into the receive path, this is controlled by an external logic level.
The FX614/MX614 may be used in a wide range of telephone systems. With a low operating voltage, a very low- current ‘sleep’ mode and an operating current of 1mA the device is ideal for portable, terminal and line powered applications. A 3.58MHz standard Xtal/Clock rate is required and the device operates from a 3.0V to 5.5V supply.
Devices are available through our Distributor Network.
1200bps half-duplex Bell 202 Compatible Modem with:
FX/MX604 and FX/MX614 FAQ
Q. Can I use the FX614 in the same circuit as an MX614 or vice versa? The FX604 and MX604 V.23 modems are also pin and function compatable with each other.
A. Yes. The FX614 and the MX614 are completely pin and function compatible so code and hardware can be re-used in new designs. Similarly the FX604 and MX604 V.23 modems are also pin and function compatible with each other so are interchangeable.
Q. 604 – Why do the FX604 and FX614 apparently receive data when there is no input signal?
A. The FSK receiver of the FX604 and FX614 has a very high sensitivity and in the absence of a valid FSK signal will decode noise as data. This is not a fault but is due to the wideband properties of noise where sufficient energy may be present within the FSK decoder’s bandwidth.
To prevent spurious reception a baseband carrier detect output (DET) is used to determine the validity of the received signal. The detector block is a simple energy detector that receives predominantly in-band energy from a band-pass filter in the device input. The DET should be monitored during reception and used to ‘intelligently’ decide whether the data is likely to valid, suspect or invalid. During periods when there is no data reception the DET will be predominantly low but is likely to false so the receiver should be powersaved where practical.
DET does not internally gate the FSK receiver because this would prevent data reception during short duration events such as fades when data recovery may still be possible.
Q. 604 – Are the FX614 and MX614 compatible with the HART specifications?
A. Yes they are, the FX614 and MX614 both appear to be suitable for encoding and decoding HART signals but have not been specifically designed to do so.
But just to add some further points:
Q. 604 – Does CML offer a suitable replacement device for the TCM3105 (Bell202) modem application?
A. CML has several devices that can comply to the Bell202 specification: FX614 / CMX624 / CMX850 / CMX866 / CMX867A / CMX868A an B / CMX869A and B / CMX878.
The FX614 is a very popular device which is used as a suitable replacement for the TCM3105.
The FX614 offers a cheap and simple solution to wire-line and radio modem applications.
Please refer to the following publication for a simple cheap amateur radio solution using the MX614_TCM3105_article.