Polycom RS-232 manual Wildcard Characters, Using Acknowledgements

3.2. Wildcard Characters

The use of the wildcard character, '*', can make programming the host controller much easier. Be careful when using wildcards, however, since they can generate a lot of traffic on the digital bus.

3.3. Using Acknowledgements

It is a good idea for the host program or control system to make sure that all connected Vortex devices have acknowledgment mode enabled (see the ACKMOD command). When acknowledgment

mode is on, a Vortex device will send an acknowledgment for each command it receives. Proper use of acknowledgments makes the host program more robust and makes supporting multiple hosts effortless. The rest of this section describes how to use acknowledgments to achieve these goals.

As a convenient example, let us imagine a host program with a graphical user interface (GUI). The user presses buttons on the GUI to enable or disable features of various linked Vortex devices. The buttons on the GUI reflect the current status of the corresponding feature.

When the user presses a button on the GUI to enable or disable a feature, the host program should send the corresponding command to the selected Vortex device. It may be tempting to update the status of the GUI button at this point, but this can cause problems if there are transmission errors or if there are multiple host controllers. The proper way to handle this is to only update the GUI controls based on acknowledgments received from the Vortex device.

To implement this, organize your code so that the functions that send commands are totally separate from the functions that receive responses from the Vortex devices. This also enables your host program to support the presence of multiple host controllers. For example, consider the following sequence of events.

1.Another host sends a command to a Vortex device.

2.The Vortex device responds with an acknowledgment that is broadcast to all of the other hosts.

3.Your host program receives the acknowledgment and updates the status of the corresponding control.

The result of this programming model is that all hosts and linked Vortex devices will always be synchronized.

For simple on/off features, your host program can make use of the toggle arguments to some commands (e.g., 'SSEN2'). By sending a toggle command when a button is pressed, and updating the button based on acknowledgments, your host program will not have to keep track of the status of the button.

In a similar fashion, many of the integer commands (such as gains) can be controlled by incrementing or decrementing them by a specific amount. For example, the command 'GAINIA>1 ' increments the input gain on channel A by 1 dB. The acknowledgment for this command will return the actual value that the gain was incremented to. Thus, to implement a volume control, your control program can send a command to increment the gain by 1 dB when the "up" button is pressed and decrement the gain by 1 dB when the "down" button is pressed. The control can update its level indicator based on the acknowledgment that is received.