Rockwell Automation 2755-DM9, -DM9E High Speed Decoder - Manual (Page 56)

Chapter 4
Configuring Your Decoder
4–29
When you set the decoder trigger mode to package detect and send data
packets to the host, you must take into consideration the length of the
package detect signal, the package rate, and the transmission time. The
decoder is able to generate data at a rate that is much faster than the
transmission rate. Therefore, at high package rates the decoded data can
exceed the speed at which the data is transmitted. Refer to Figure 4.3.
P = A + B = Time from one package to the next.
A = Trigger Active period. Refer to Input Filter description for timing
considerations.
B = Time between packages. This must be a minimum of 5 msec without the
package detect filter enabled, and 15 msec with the package detect filter
enabled.
For long message packets, allow additional time to prevent loss of data
due to a buffer overflow. When the no-read timer is disabled, the time
needed between packages can be calculated as follows.
6 x (Number of Characters)
Baud Rate ( where Baud rate is
≥
9600)
When the no-read timer is enabled, the time required between
packages can be calculated as follows:
6 x (Number of Characters)
Baud Rate ( where Baud rate is
≥
9600)
Figure 4.3
Package Detect Timing with Communications Enabled
B
P
A
B =
+ (No-Read Timer ) - A B =