FSK Modem and DTMF Codec
• V.23 1200/75, 1200/1200, 75, 1200 bps FSK • Wireless Local Loops
• Bell 202 1200/150, 1200/1200, 150, 1200 bps FSK • SMS Phones
• Bell 103 300/300 bps FSK • Security Systems
• Low Voice Falsing DTMF Decoder • Remote Utility Meter Reading
• DTMF/Tones Transmit and Receive • Industrial Control Systems
• Low Power - High Performance • Pay-Phones
• Software and Hardware Compatible with CMX86x
Family of Wireline Products
• Set-Top Boxes
• Wireless Local Loop
• SMS Phones
• Security Systems
• Remote Utility Meter Reading
• Industrial Control Systems
• Set-Top Boxes
The CMX865 is a multi-standard modem for use in telephone based information and telemetry systems.Control of the device is via a simple high speed serial bus, compatible with most types of μC serialinterface. The data transmitted and received by the modem is also transferred over the same serial bus.
On-chip programmable Tx and Rx USARTs are provided for use with asynchronous data and allow unformatted synchronous data to be received or transmitted as 8-bit words.
A high-quality DTMF decoder with excellent immunity to falsing on voice and a standard DTMF encoder are included. Alternatively, these blocks can be used to transmit and detect user-specific, programmed
single and dual-tone signals, call progress signals or modem calling and answering tones.
Flexible line driver and receive hybrid circuits are integrated on chip, requiring only passive external
components to build a 2 or 4-wire line interface.
The device also features a Hook Switch Relay Drive output and a Ring Detector circuit which continues to function when the device is in the powersave mode, providing an interrupt which can be used to wake up the host μController when line voltage reversal or ringing is detected.
The CMX865 operates from a single 3.0 to 3.6V supply over a temperature range of -40°C to +85°C and
is available in a 24-pin SOIC package.
Design Support Information
CMX865 and CMX865A FAQ
Q. CMX865A: The DTMF de-response is given as 30ms max but I measure more than this on some DTMF digits under certain conditions.
A. The de-response time of the DTMF decoder is correct.
The programmer cannot see the DTMF response/de-response directly. What the programmer sees is b5 which loosely tracks the DTMF decoder response.
When a DTMF digit ends, the DTMF decoder will de-respond and some time later b5 will signal this by going low.
To allow for polling, the minimum time that b5 is high is 14ms. To ensure that short DTMF digits with short gaps between can be detected in the code, b5 will de-respond when energy from the following tone is detected. Under these conditions the maximum high time for b5 is 30ms. This maximum high time is called the DTMF de-response time.
Note that with longer DTMF tones and longer gaps, b5 can be high for more than 30ms.
This downloadable graphic shows the response of b5 in a number of different receive scenarios.
Q. Can you detail the differences of the CMX865A with respect to the CMX865?
A. The listings below should help you:
CMX865A Advantages over CMX865
Smaller package, less pins = smaller footprint
Pin count reduced from 24 to 16
V.21 function added
CMX865A Functional Difference from the CMX865
The RT and RD pins are removed. The ring detector function is not required in Wireless Local Loops and most alarm systems.
This function is easily provided by a GPI/O pin on the host micrprocessor.
Schematics are available from CML Tech Support.
The hookswitch pin is not present. This is a simple output function that is more cost-effective when moved to the host processor.
The receiver interface has been simplified by making it single-ended.
The internal hybrid function eliminates the need for a differential receiver.
V.21 transceive capability has been instated for alarm panels and other niche applications
6.144MHz operation only
A series of Application Notes to assist with design-ins to the target markets
Can be evaluated in the EV8600 Modem Evaluation Kit
An adapter board, HB865A, is available to allow device evaluation in a dual-in-line footprint
The CMX865A is designed to interface easily to a SLIC.
All of the transmit signals are summed within the device and there is a register for software setting the output signal level (the same as the CMX865). The output can be single-ended or differential.
The outputs tri-state automatically when the modem is not being used thus providing a high impedance to the line. This allows simple mixing of other signals, such as voice.
The input is single-ended with a gain-setting, feedback path for convenience.
Like the CMX865, the CMX865A also has a software controlled attenuator.
The CMX865A will provide exactly the same signalling as the CMX865 and is directly register compatible
The operating voltage is the same as the CMX865 but the operating current is expected to be slightly lower