Dranetz Visa Guia do Utilizador descarregar pdf (Página 188)

9-8

External Communication Interface, continued

Connection

setup via

Modem

(continued)

Back at the PowerVisa, the last step in configuring the modem communications is to

modify the modem initialization string to match the modems and chipsets being used.

The goal is to configure for the following:

• Restore factory settings.

• Set auto-answer to answer on one or two rings (more than two rings are allowed but

at some point the number of rings may start to conflict with NodeLink

timeouts).

• Turn hardware flow control off since you are using a "two-wire" connection (fiber

optic port).

• Set a modem inactivity timeout of 60 seconds. The modem will hang up after one

minute of continuous inactivity on the line.

• Select the minimum allowable baud rate.

Follow the steps below to change the modem initialization string. See Chapter 4

Instrument Settings - Communications for the PowerVisa screen interface.

1. From the PowerVisa Communications Settings screen used to configure modem

connection speed, click on the Change button to the right of the string field display.

2. Use the virtual keypad that appears on the screen to change and enter the new string

command. The modem initialization string commands for the Conexant (Rockwell)

chipset and the Agere (Lucent) chipset are discussed in the next section.

3. When done, click on OK to accept changes in modem communications settings.

Modem

initialization

string command

The following is the AT initialization string for a modem using the newer Conexant

(Rockwell) chipset:

AT&F;S0=2;+IFC=0,0;S30=6

Where:

AT is the modem attention command

&F instructs the modem to restore factory configuration

S0=2 turns auto-answer on and sets the number of rings to answer to two.

+IFC=0,0 turns flow control off.

S30=6 sets a 60 second inactivity modem hang up timeout.

; is a command delimiter.

NOTE: It may be necessary to adjust the modem connection speeds to specify a

minimum baud rate. This is possible using the +MS modem command. Check the

modem manual for use of the +MS command. There are several varieties of the

command. Typically, a modem modulation scheme and minimum and maximum

transmit and receive speeds can be specified. Using Hyperterminal, it is possible to get

a list of the possible command ranges and syntax by typing AT+MS=?.

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