ISDN Data and Telephony Protocol Engine (inc. X.25)
CMX228
1.5.2 Initialisation
On power-up, the CMX228 assumes its default values, which are factory programmed into the
firmware. It then performs a self-test, during which all of the LED pins and the ILFI pin are held high
for 3s. If the test is unsuccessful, the CMX228 remains in this condition.
If the test is successful, the CMX228 reads its preset values from the attached EEPROM and
examines the state of the ISDN link (ie Layer 1) before commencing normal operation. On power-up,
the ISDN link is de-activated, the POTS port is assumed to be on-hook, ringing is disabled and the
RS232 port is in the Hayes command state.
1.5.3 ISDN Interface
Simultaneous voice and data calls are possible but only one of each type. If a call is active (eg
ringing, connected or clearing down) and an incoming call of the same type (data or voice) is received,
that call will be rejected with user busy as the cause. Incoming calls are firstly checked for other calls
present, then the MSN is checked for validity, then the channel mapping, so that responses will be
handled accordingly.
When channel mapping is enabled, outgoing calls will request the channel enabled. When not
enabled, a request for any channel is made. If no free channels are available for outgoing calls, a
locally generated busy tone is returned to the analogue port or the appropriate Data Call Result Code
is returned to the digital port.
1.5.3.1 Activation
Activation occurs in the following circumstances:
·
·
·
The ISDN network activates.
The device connected to the analogue port goes off hook.
The device connected to the data port sends a Hayes dial command.
The Terminal Endpoint Identifier (TEI) is either negotiated (Hayes register !C7 = 64) or fixed (Hayes
register !C7 = 0 to 63). Line powering of the CMX228 is not supported.
The 'AR' indicator (LED8) toggles between high and low states when the CMX228 is powered up, and
remains constantly low once the CMX228 identifies an activated ISDN line.
ISDN line power detection is not implemented and the CMX228 will negotiate a new TEI on any new
network activation.
1.5.3.2 De-activation or Line Disconnection
De-activation or line disconnection causes the TEI to be removed. Upon re-connection the CMX228
will only be re-activated and request a new TEI when one of the conditions in the above section is met.
1.5.3.3 Line Failure Detection
If the line failure detection parameter is enabled (either via the POTS port or via the RS232 interface)
the CMX228 will check that Layer 2 communications are active every sample period of 30 seconds. If
Layer 2 communications are not active, the CMX228 will attempt to activate them. If they remain
inactive for 2 sample periods, the line is deemed to have failed, so then the ILFI pin is set high. The
CMX228 continues to attempt to activate the line and if it becomes active and stays active for 2
sample periods, then the ILFI pin is set low.
ã 1999 Consumer Microcircuits Limited
ã 1999 Chiron Technology Limited
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D/228/1
CMLMICRO [ CML MICROCIRCUITS ]
