Campbell SAT ARGOS Manual do Utilizador descarregar pdf (Página 94)

ZENO

-3200 USER MANUAL

Coastal Environmental Systems (206) 682-6048

Page 86

We also recommend that you force the baud rate between the two modems to 9600 baud. This is the first

command in the table above. This ensures that there can be no data overruns.

103

Auto-Answer On

Auto-Answer is the parameter that describes whether and when the modem picks up incoming calls.

For modems that are on continuously, in order to dial up the ZENO

-3200 and communicate with it, you

must switch Auto-Answer on.

104

For low-power (power-controlled) modems, this is unimportant since the ring-detect line is connected

directly to the ZENO-3200 and not the modem circuitry itself.

Suppress Result Codes

Typically, when you send a command to a modem, it gives a result code as a response. for example, if

you send the attention string AT, the modem typically responds with OK.

When you connect a modem to a ZENO

-3200, it is important to turn the

result codes off as the ZENO

-3200 may respond to result codes from the

modem.

If the result codes are not turned off from the modem, a possible infinite loop of communications between

the ZENO

-3200 and the modem may occur.

For example, suppose that you hang up a modem connection while in the middle of downloading data

from the ZENO

-3200. The ZENO

-3200 continues to send data out from its COM port. The modem

receives that data, interprets it as an invalid command, and sends the response ERROR. The ZENO

-3200

receives that response, interprets that response as an invalid command, and sends an error message back

to the modem. This loop can carry on indefinitely. The solution is to switch off all modem result codes.

DCD follows remote carrier

The modem at the ZENO

-3200 monitors the carrier signal over the telephone lines. This signal indicates

that there is a good connection between the two modems. When the carrier signal drops, the modem at

the ZENO

-3200 hangs up. The option “DCD follows remote carrier” specifies that the modem also sets

the DCD line low at this stage.

105

The ZENO

-3200 continually monitors the DCD line to determine whether there is a possibility of

incoming commands. When DCD is asserted, the ZENO

-3200 wakes up and powers up the serial port.

This means that the ZENO

-3200 is drawing several tens of milliamps, rather than the few milliamps it

draws in sleep mode. for battery-powered installations, it is important that the ZENO

-3200 remain in its

sleep mode when possible. Therefore, the DCD line should be set to drop when the modem hangs up.

The command "DCD follows remote carrier" will ensure that it hangs up properly.

103

This can be an issue if you use modems of different types at either end, where either one may not have speed

detection and/or fall back capability.

104

Most modems are shipped with the factory setting Auto-Answer off as a security feature. This avoids your

computer being unexpectedly called up.

105

The alternative is that the modem always asserts DCD.

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