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CMX635

ISDN Subscriber Processor

CML Microsystems Plc 

ISDN Subscriber Processor

CMX635

1.5 Functional Description

The CMX635 is a highly integrated ISDN Subscriber Processor that allows low chip count systems

to be designed for a wide variety of ISDN voice/data terminals and POTS terminal adaptors. It

can also provide the majority of functions required to implement an intelligent NT or NT1Plus

system.

The CMX635 incorporates a 4-wire ST interface, which conforms fully to the ITU-T I.430 and

ETS 300 012-1 specifications. It provides the necessary layer-1 control to implement both the TE

and NT ends of the ST reference point and the layer-2 controls to implement the D-channel

signalling layer.

HDLC Controllers and associated FIFOs are provided for the B1, B2 and D-channels. The

Controllers can be configured to automatically process the bit stuffing, flag generation/recognition,

address matching and CRC generation/checking required to support the ITU Q.921 protocol

reducing the software overhead on the host processor. The automatic processing can be

progressively disabled until fully transparent operation is achieved with corresponding increased

processor load. The data FIFOs are implemented as a 1024 byte RAM that can be flexibly

partitioned to form the 6 required FIFOs (2B+D, Receive and Transmit), enabling optimum FIFO

size to be selected for the application.

An IOM-2TM /GCI interface is provided to enable operation with other IOM compliant devices. This

facility can be used to connect to a ‘U’ Interface device in NT mode of operation or to expand the

number of POTS ports in TE mode by connection to devices such as the CMX625 – ISDN TA

POTS Interface. The IOM interface can be configured as a timing master or slave for TE or NT

applications respectively and has full Mult-Framing capabilities.

The CMX635 has the functions necessary for operation as an ISDN feature phone with

speakerphone capability or as a POTS terminal adapter. There are 2 independent uncommitted

differential input amplifiers suitable for connection to 2 microphones for feature-phone

applications or to a SLIC/POTS hybrid for POTS operation. A 100mW power amplifier is provided

to drive a speaker for feature-phones or the ring input to a SLIC for POTS. An additional output is

provided to drive a handset earpiece or the SLIC/Hybrid input for POTS.

Sophisticated speakerphone operation can be implemented using the digital noise and voice

filters available in the CMX635 in conjunction with user supplied software algorithms.

For POTS operation a DTMF decoder enables interpretation of dialling information and can also

be configured to detect far end DTMF tones. A tone generator supplies all of the necessary tone

frequencies for call progress tones. Other tone standards supported are: Fax and Modem ‘answer’

and ‘originate’, ITU (CCITT) ‘R1’ and ‘R2’ signals, and sufficient tones for simple melody

generation.

Caller Line ID (CLID) and Caller ID on Call Waiting (CIDCW) functionality can be emulated using

the tone generator and the FSK UART facility.

A Subscriber Pulse Metering (SPM) output is provided to enable operation with POTS legacy

payphone equipment. The frequency standard can be set to either 12kHz or 16kHz.

A DTMF generator is available to allow feature-phone equipment to generate comfort dial tones

and to enable control of remote DTMF signalling and Menuing systems.

The µController interface is compatible with multiplexed and non-multiplexed address/data

busses and generic Motorola and Intel style control. The CMX635 will automatically detect which

style of interface is being used and configure itself accordingly.

© 2001 Consumer Microcircuits Limited

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D/635/2

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