Campbell SAT ARGOS Manual do Utilizador descarregar pdf (Página 100)

ZENO

-3200 USER MANUAL

Coastal Environmental Systems (206) 682-6048

Page 92

Configuring and using the UDP PAD service requires familiarity with AT

commands. In particular, an understanding of the +WS registers from

+WS60 to +WS74 (as described in the AT Command Reference Manual) is

essential.

The Sierra Wireless MP200 has two states: the command state and the data state. When the UDP PAD

service is selected (+WS45=0), the modem is in command state. The data state will be entered when a call

is originated by dialing or the cellular modem answers an incoming packet (call).

Escaping Data State Using TIES

The Time Independent Escape Sequence (TIES) is a method to shift the cellular modem from the data

state to the command state. It is enabled by setting register +WS60=1 (the default).

The escape sequence is the string AT+++, ending with the Primary Forwarding Character (defined by

included in the TIES checking.

CDPD Dialing Out – Client Sessions

The Sierra Wireless MP200 can be used to originate a UDP session by “dialing” an IP address and port

using the ATD[ip_address.port] command. The modem will only answer calls addressed to port

2100. The modem will go on-line (into data state) and wait for a packet to send or one to arrive. While the

session is open, only traffic from the dialed server will be accepted by the MP200.

The local host (the ZENO

-3200) can compose packets and forward them to the network. Packets from

the called server will be delivered to the local host.

To close the session, the local host must leave data state by issuing the TIES or toggling DTR (if

configured with (AT&D1 or AT&D2) followed by a “hang up” using the ATH command.

CDPD Answering a Call – Server Sessions

The Sierra Wireless MP200 cellular modem can be configured to auto-answer incoming packets by

opening a session when a packet arrives. This is handled by setting ATS0=1. The MP200 will open a

session and enter the data state when a packet addressed to the cellular modem’s IP address arrives on any

port.

When a packet arrives, the modem sends the CONNECT message, enters the data state, and sends the

packet to the local host (the ZENO

-3200). Again, the cellular modem will remain in the data state until

the local host issues the TIES or toggling DTR (if configured with AT&D1 or AT&D2) followed by a

“hang up” using the ATH command.

CDPD Packet Assembly

A packet is started and buffered when the local host starts sending data to the cellular modem. If the

buffer reaches the maximum packet length, the packet is forwarded and a new packet is started.

The modem can echo characters sent from the local host if register +WS62=1 and, in cases where

terminal emulation program is being used, it allows typing and sending messages in real time.

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Campbell SAT ARGOS Manual do Utilizador Página 100