CMX228S1 MX-COM, Inc., CMX228S1 Datasheet - Page 8

• Manufacturer Part Number: CMX228S1
• Description: ISDN data and telephony protocol engine with x.25
• Manufacturer: MX-COM, Inc.

ISDN Data and Telephony Protocol Engine with x.25
8
CMX228 Advance Information
4.
General Description
The CMX228 is a single-chip data processor which has been mask programmed with firmware to implement
an ISDN protocol stack. This enables the CMX228 to interface an analog (POTS) port and a digital (RS232)
port to 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 CMX228 is intended for use as part of an ISDN chipset and all descriptions in this data sheet refer to this
implementation, which is shown 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 CMX228 interfaces with a CMX605 Tone Generator and DTMF Receiver chip, which decodes incoming
DTMF tones and generates certain call progress signals (e.g. busy tone) normally originating from an analog
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 CMX228 also provides a data port that 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, X.25 protocol on both B and D-channels,
packet assembly and disassembly for X.25, and a comprehensive set of Hayes commands (which facilitate
the use of normal PC-based modem software). The CMX228 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 CMX228 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 CMX228 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 4.8. Further
details are available on completion of a Non-Disclosure Agreement. Please contact MX-COM directly for
further details.
The firmware and finite state machine embedded in the CMX228 have been used in products that have
gained ETSI CTR3 approval.
MX-COM, Inc
2000 MX-COM, Inc.
4800 Bethania Station Road, Winston-Salem, NC, 27105-1201, USA
Doc. # 20480216.001
www.mxcom.com tel: [phone] 744 5050 fax: [phone]
2000 Chiron Technology Limited
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