ISDN Data and Telephony Protocol Engine (no X.25)
CMX218
1.5
General Description
The CMX218 is a single-chip data processor which has been mask programmed with firmware to
implement an ISDN protocol stack. This enables the CMX218 to provide an analogue (POTS) port
and a digital (RS232) port with an ISDN S-bus network connection. Key variables are stored in an
external EEPROM and the user can provide additional features by adding external ROM and RAM.
Access to the firmware Application Programmer's Interface (API) facilitates the seamless integration of
the user's additional features with the pre-programmed ISDN to POTS and RS232 interfaces.
The CMX218 is intended for use as part of an ISDN chipset and all descriptions in this data sheet refer
to this implementation, which is shown diagrammatically in Figure 3. The use of alternative chipsets is
not supported.
The firmware supports connection to an ISDN S-bus network interface via the Siemens PSB21525
HDLC controller and the AMD AM79C30 ST controller with integral PCM codec for a single POTS
port.
The CMX218 interfaces with a CMX605 Tone Generator and DTMF Receiver chip, which decodes
incoming DTMF tones and generates call progress signals (eg busy tone) normally originating from an
analogue telephone exchange. The firmware translates the CMX605 data into ISDN D-channel
commands and vice versa to support both incoming and outgoing calls. For the ISDN interface, D-
channel commands sufficient for standard telephony applications are implemented. With the aid of a
small amount of discrete circuitry, exchange battery voltage, ringing current, line reversal and off-hook
detection are also supported, to complete the POTS interface.
The CMX218 also provides a data port which can drive a standard RS232 interface with the aid of a
Maxim MAX238, or similar, level converter. The firmware provides support for incoming and outgoing
data calls, RS232 auto-bauding from 9600bps to 115200bps, auto parity detection, RTS/CTS flow
control, call clearing on loss of DTR, V.120 rate adaption, PPP async to sync conversion and a
comprehensive set of Hayes commands (which facilitate the use of normal PC-based modem
software). The CMX218 has dedicated outputs for visible indicators (LEDs) which can be used to
provide information on the call status. Support for Multiple Subscriber Numbering is also included in
the firmware.
The CMX218 can be configured either by means of keypad (DTMF) programming via the POTS port
or by means of an extended Hayes command set via the RS232 port. Configuration parameters allow
the user to change (for example) the format and cadence of the ringing signal, so as to facilitate use of
the CMX218 in different countries. Each POTS and RS232 interface is able to configure the variables
relevant to its own use.
An Application Programmer's Interface (API) is available and is described separately in section 1.5.8.
Further details are available on completion of a Non-Disclosure Agreement. Please contact CML
Sales directly for further details.
The firmware and finite state machine embedded in the CMX218 have been used in products which
have gained ETSI CTR3 approval.
©
1999
Consumer Microcircuits Limited
©
1999
Chiron Technology Limited
9
D/218/1
CMLMICRO [ CML MICROCIRCUITS ]
