Dranetz Visa Uživatelská příručka stáhnout pdf (Strana 186)

9-6

External Communication Interface, continued

Connection

setup via

Modem

When configuring both the PowerVisa and NodeLink

for modem communications,

keep in mind that the PowerVisa uses a fiber optic serial port in order to maintain

electrical isolation. This means that there are no control signals available to a modem

to use for handshaking and flow control.

It is highly recommended that identical modems be used on the PowerVisa and the

computer. Identical modems will have the same internal buffering and are more likely

to negotiate modulation, speed, and error correction suitable to both modems. If the

modems used are not identical then both the PowerVisa and the computer should have

modems with the same chipset (i.e. Rockwell, Lucent).

When configuring for modem communications, the first decision to be made is the port

speed for both ends of the communications link. This is the speed at which the

PowerVisa communicates with its modem and the speed at which the computer

communicates with its modem. The same speed should be chosen for both. Ideally the

speed should be at or just below the anticipated modem connect speed. Since most

modems today will attempt to connect at least at 56 kbps, 38.4 kbps would be a good

choice for the two port speeds. This helps to prevent possible modem buffer overflow.

Follow the steps below to configure the PowerVisa for a port speed of 38.4 kbps. See

Chapter 4 Instrument Settings - Communications for the PowerVisa screen interface.

1. Connect the modem to the PowerVisa communications adapter.

2. Turn on the modem.

3. From the PowerVisa home screen, click on the Preferences icon.

4. Choose Communications from the Instrument Settings Setup Menu.

5. Verify that both the Enable Communications and External Modem Connected

checkboxes are enabled (checkboxes checked).

6. Check to enable 38400 under Baud Rate (bps).

NOTE: The port speed of 38400 (38.4 kbps) used above may be substituted with

57600. Experiment to find the maximum port speeds that will work for the system.

7. Note the modem initialization string at the bottom of the screen. Do not exit this

screen yet since you may be modifying this string after you have the Windows

modem

configured.

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