KEYENCE N-400 - Manual (Page 91)

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Chapter 4 Multi-Drop Link Mode Control Procedure
4
Baud rate (for RS-485) Communication time (b)
Number of data Number of data Number of data
digits: 10 digits: 20 digits: 32
9600 bps 64 ms 74 ms 86 ms
38400 bps 28 ms 32 ms 37 ms
4.6 Communication Time Consideration
This section describes how to calculate the time required for data transmission and
for command transmission in multi-drop link mode.
■ How to calculate data transmission time
The following is the timing chart for multi-drop link mode communication .
Through the RS-485 communication between the N-400 and each BL series unit,
data transmission is constantly performed from the BL series to the N-400.
When the N-400 sends the polling command to a BL series with a specified ID
number, the data read by the BL series is sent to the host computer through the
RS-232C interface of the N-400.
* The above timing chart shows the case in which five BL series units are con-
nected.
Therefore, data transmission is delayed by a certain time duration until the polling
command is sent to the BL series after the BL series reads bar code data.
First, obtain the time duration required for the RS-485 data transmission.
In the RS-485 data transmission from the BL series to the N-400, the required time
varies depending on whether the BL series has stored bar code data (the BL series
has already read bar code data) or not.
In the above timing chart, “a” (the RS-485 data transmission time is short) shows
the case in which the BL series has stored no data, and “b” (the RS-485 data
transmission time is long) shows the case in which the BL series has stored some
data.
• a: RS-485 data transmission time required when the BL series has stored no
data
• b: RS-485 data transmission time required when the BL series has stored some
data
Baud rate (for RS-485) Communication time (a)
9600 bps 27.9 ms
38400 bps 12.8 ms
N400
(RS-485)
BL
N400
(RS-232C)
Host
1 2 3 1 2 3 4 4 5 1 1 2 3 2 3 4 5 5
b a
A A
B B