User's Guide

User’s Guide CDPD Operation
2110059 Rev 1.0 Proprietary and Confidential Page 51
5.8. Packet Assembly Management
Once in data state with either the UDP or TCP PAD enabled, the modem accepts data from the
host (DTE) and assembles it into packets. Packet assembly is largely transparent to the host but
some assembly management features are available.
Starting a Packet
A packet is started when the host starts sending data to the modem. The modem will buffer the
data as it assembles the packet.
Real Time Data Entry and Editing
The modem can echo characters from the host back to it is cases where a terminal application is
being used to allow individuals to type and send messages in real time. This is similar to Internet
Relay Chat (IRC). Setting +WS62=1 will enable the echo (the default) and setting +WS62=0
will disable it.
If this type of communication is being used, the modem can also optionally allow editing of the
packet buffer. Setting +WS72=1 (the default) will enable local editing of the data before it is
forwarded to the network. This allows you to backspace using the character set in +WS73 (the
default is 8 <BS>). If local echo is also enabled then the modem will echo the backspace
character, a space, and another backspace.
Forwarding a Packet
The modem closes and sends a packet when one of the following events occur:
1. The maximum packet length set in +WS74 (default 1000) is reached. You may wish to set
this value smaller if you are encountering too many packet errors and retransmissions. Setting
it below 5 will preclude use of the TIES to exit data mode. See below for details.
2. The modem receives the PAD Primary Forwarding Character set in register +WS64. This
character defaults to 13, the carriage return <CR>. The feature is enabled by default and can
be controlled with a bit mask option set in register +WS63. The options are:
0 Disabled
1 The packet is terminated and the forwarding character is discarded.
3 The forwarding character is included in the packet before the packet is closed and sent.
The default option setting is 3.
3. The PAD Inter-Character Timer (+WS70) expires. This timer is disabled (set to 0) by
default. It can be set to values from 0.1 to 25.5 seconds. If particularly short times are used,
real time typing will be forwarded virtually as it is received. This would also mean that
manually typing the TIES to escape data mode is virtually impossible as the packet is closed
before the full character string is entered.
NOTE: If you disable the primary forwarding character (+WS63=0) and the timer (+WS70=0),
the only way to forward packets will be to fill the packet buffer. This is very strongly
discouraged.
Using TIES
The Time Independent Escape Sequence (TIES) is a method to shift the modem from data state to
command state. It is enabled by setting +WS60=1 (the default) and disabled by setting
+WS60=0.
The escape sequence is a packet containing only the string “AT+++” where the “AT” must be in
uppercase. To ensure the packet contains only this value you must be sure that you are starting a
new packet and that the modem will not close the packet before the string is complete.
To ensure you are starting a packet, you must ensure that one of the forwarding events described
above has occurred. The easiest way is to send the Primary Forwarding Character.
To ensure that you can enter the complete string, you cannot set the maximum packet length less
than 5. You must also provide sufficient time in the PAD Inter-Character Timer to enter each