ISDN Data and Telephony Protocol Engine (inc. X.25)
CMX228
The escape sequence ‘+++’ (with Guard Time = 1s before and after the sequence) will cause the
CMX228 to enter the command state from the data state and to return an ‘OK’ response. Sending an
ATO command will be ignored, ie the CMX228 remains in the command state.
The following is a more detailed description of the Hayes commands listed above:
A (Answer)
Format:ATA<CR>
Causes the CMX228 to answer an incoming data call, by sending a CONNECT message to the
network. If a CONNECT ACK is received the CMX228 enters the data state after returning a
‘CONNECT XXX’ result code to the DTE on the RS232 port (where the XXX is the speed in baud). If
a RELEASE, RELEASE COMPLETE or DISCONNECT message is received a ‘NO CARRIER’ result
code is returned. The command is not valid if there is no incoming call and it will return ‘ERROR’.
D (Dial)
Format:ATD{DN}<CR>
Format:ATDT{DN}<CR>
Format:ATDP{DN}<CR>
{DN} is a directory number of up to 23 ASCII characters from 0..9, Sand #. This form of the ATD
command causes an outgoing SETUP message to be sent to the network with a Called Party Number
Information Element which contains the digits included in the command. Any commands that follow
this command are ignored.
If the CMX228 receives any character from the DTE after an ATD command, which causes a SETUP
message to be sent to the network, and before the call is connected, the attempt to make a call is
abandoned, ie a DISCONNECT message will be sent to the network and a ‘NO CARRIER’ result code
returned.
Calls are established with the D command, irrespective of the state of the DTR pin. The result code
response is either:
'CONNECT'
'NO CARRIER'
'NO DIALTONE'
'BUSY'
- call successful. The CMX228 will automatically enter the data state.
- call rejected by the remote user or the network
- ISDN link down
- remote user busy and other causes
Calls are cleared in the following way:
(i) The remote end or network clears the call by sending a DISCONNECT message or the ISDN
line fails/is removed: 'NO CARRIER' is sent to DTE.
(ii) DTR is dropped (with a de-bounce period of 50ms) by DTE causing the CMX228 to send a
DISCONNECT message to the network and enter the disconnect state, awaiting a RELEASE
COMPLETE from the network. The CMX228 sends the 'OK' response when clearing of the ISDN
call is complete ie RELEASE and RELEASE COMPLETE messages have been transmitted
across the network, (dependant upon the state of &D command).
(iii) The DTE issues the escape sequence ‘+++ ‘(with Guard Time = 1s before and after the
sequence), receives an 'OK' response and then issues the Hang-up command (see section on H
command below). The CMX228 sends the 'OK' response when clearing of the ISDN call is
complete.
ã 1999 Consumer Microcircuits Limited
ã 1999 Chiron Technology Limited
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CMLMICRO [ CML MICROCIRCUITS ]
