KEYENCE N-400 - Manual (Page 72)

Chapter 4 Multi-Drop Link Mode Control Procedure
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■ Transmission buffer of BL series
The BL-500/BL-180 series provides a transmission buffer that can store 400 bytes
(400 characters). This buffer temporarily stores the BL series’ data and the N-400
executes polling for the data stored in this buffer. The data is stored until polling is
executed.
Five characters per piece of data indicating the data attributes are added to the
number of characters of the data (including the additional data such as number of
decodings) when stored in the transmission buffer .
Example 1
When the number of bar code digits is 10 (with no additional data)
400 / (10 + 5) = 26
The transmission buffer can store 26 pieces of data.
Example 2
When the number of bar code digits is 20 (with no additional data)
400 / (20 + 5) = 16
The transmission buffer can store 16 pieces of data.
If the number of read data exceeds the buffer capacity, the BL series until causing
the BUFFER OVERFLOW error sends the following error code to the host compu-
ter, and clears all data stored in the BL series.
The other BL series units which did not cause the error can continue to operate
normally.
* mm = 01 to 31: ID number of BL series
The BUFFER OVERFLOW error occurs when the BL series’ reading interval is
shorter than the polling interval. To prevent this error, take the following actions:
• Reduce the polling interval by setting the baud rate to 38400 bps (the highest
rate) for the RS-485 communication between the N-400 and each BL series
unit.
• Reduce the polling interval by reducing the number of connected BL series
units.
• Reduce the amount of data to be processed by the N-400 by increasing the BL
series’ reading interval.
• In manual polling mode, modify the program so that the polling command is
sent to the BL series before the BUFFER OVERFLOW error occurs with the BL
series.
• Erase all ID numbers of disconnected BL series on the “ID SETUP” screen of
the N-400 setup software.
% P mm CR , % STX P mm ETX