B&B Electronics ESR904W Adjusting the Behavior of Device Communication Ports, Polling Strings

Device Communication Ports

Chapter 5: Adjusting the Behavior of Device Communication Ports

There is a significant difference between serial and Ethernet data communications. Data that comes in through the Ethernet is presented to the device in the form of very distinct packets. On the other hand without information about the format of the data coming in through the serial port the device may not know at what point to package up the data and hand it off to the Ethernet network. It is for this reason that the ESR90xW series of devices allow you to define when the device converts serial stream data into Ethernet packets. The following examples are provided to illustrate the power behind these options:

Configuration #1: The ESR90xW is connected to a device used to monitor air temperature. Software that interfaces with this hardware polls the device for the current status once a minute. This data is returned in the form of a single byte containing the temperature in Celsius.

Configuration #2: This ESR90xW is connected to a machine is connected to an ATM machine. When a customer starts a transaction with the ATM a large burst of serial data is passed onto the central bank.

Obviously in both of the configurations the data is critical and needs to be passed over the network in the quickest manner possible. For configuration #1 the best behavior for the device would be to send the incoming byte of temperature information out over the network as soon as it comes in. On the other hand if the device acted the same way for the second configuration it would flood the network with all of the Ethernet overhead. In this case the device would be better to wait for a moment and send a full Ethernet packet rather than a packet for each byte of data.

There are a number of different conditions that your ESR90xW can be configured to watch for when dealing with the data coming in through it’s serial communication port(s).

•Polling Strings

•Timeouts

•Data Quantities

Documentation Number: ESR90xW-4905m Chapter 5 21

Device Communication Ports

Polling Strings

Polling strings are used when you want the ESR90xW to look for a specific data pattern before taking the data in it’s serial buffer and creating an Ethernet packet with it. Polling strings can be configured to monitor not only the serial traffic but the Ethernet traffic as well.

Timeouts

Polling strings are used when you want the ESR90xW to look for a specific data pattern before taking the data in its serial buffer and creating an Ethernet packet with it.

There are two different types of timeouts. Total Message and Inter-character timeouts. A Total Message timeout counter starts when the first byte is received. Once the specified amount of time has elapsed since this initial byte the trigger is fired and the device will transmit the buffered data.

The second type of timeout is an Inter-character timeout. This is used to trigger after a defined amount of inactivity.

Data Quantities

In addition to the two previously mentioned methods of Ethernet packet transmission triggers you can also setup a specific data amount that the device will wait for before acting on the incoming data.

Using Multiple Conditions

You can use the data trigger conditions individually or it is also possible to use them in combination with each other. When more than one condition is specified they are treated as a “logical AND”. This means that if any of the conditions specified is true then the data buffer is transmitted.

22 Chapter 5 Documentation Number: ESR90xW-4905m

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