User's Manual

Protocol Operation
Crescendo UHF Half-Duplex User Manual Page 36 of 78
6.4.2 Local Mode
Both point-to-point and point-to-multipoint protocol modes allow local command mode to be entered using
the escape sequence (section 6.5.3 on page 37), or by using the DTR line on the main port (section 6.5.5).
Returning to online mode is achieved using the online command (ATO). The protocol can also be configured
to start in local command mode when power is applied. For data to be transferred between two end units,
both units must be online, not in local command mode.
If the radio modem receives RF data while in local mode, it will be discarded.
6.5 Hayes Dial-up Protocol
The Hayes dial-up protocol provides a connection mechanism that emulates a PSTN modem’s dialling
mechanism. This is a more powerful method of operating than using point-to-point or point-to-multipoint
networks, as it allows dedicated communication between a base and one of many remotes.
In Hayes Dial-up protocol, the state of the connection will be reported via the RF link status parameter
(either connected or not connected). The online LED will be solid green while the connection is up. If there
is no data being transferred between the end units, background polling packets are sent to maintain the
connection.
Hayes Dial-up applications are given in section 7.2.2 on page 49.
6.5.1 Dialling
The AT commands may be used to initiate dialling of a remote radio. The ATD command is used to establish
a connection. The syntax of the ATD command is:
ATD<address><extension>
Where <address> is the address of the radio that is being dialled and <extension> is the serial port or
internal extension port that is being dialled. The available extension numbers are shown in Table 16.
Extension
Name
Description
00
Main Port
Establishes a connection between the current serial
port and the main port on the remote unit.
01
Auxiliary Port
Establishes a connection between the current serial
port and the auxiliary port on the remote unit.
Table 16: Hayes dial-up extension numbers
If the radio receives a character on the serial port while dialling is in progress, it will immediately terminate
the connection attempt and issue a NO CARRIER response message.
If a connection is established then the CONNECT response message will be returned.
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