KEYENCE N-400 - Manual (Page 73)

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Chapter 4 Multi-Drop Link Mode Control Procedure
4
4.2.4 Handshaking protocol
The N-400 supports the following four types of data communication modes
(handshaking protocols).
The handshaking protocols described in the following sections are common to both
auto polling mode and manual polling mode.
No handshaking
• The N-400 automatically sends read data to the host computer without using any
handshaking protocol.
PASS/RTRY protocol
• After sending read data to the host computer, the N-400 waits for the response
(PASS or RTRY) from the host computer.
When the host computer sends the “PASS (quit)” command to the N-400,
communication of one piece of data is completed, and the N-400 is ready to
send the next data.
The N-400 sends back no data in response to the “PASS” command.
• If the “RTRY” (request to re-send) command is sent to the N-400 while the N-
400 is waiting for the “PASS” command, the N-400 sends the same data again,
and waits for the “PASS” command.
After the N-400 receives the “PASS” command, the N-400 sends back no data
even if the “RTRY” command is sent to the N-400.
• The BL series can read bar code data even when the N-400 is waiting for the
“PASS” command. In this case, the read data is stored in the transmission buffer
of the N-400. (
➮ For the capacity of the transmission buffer, see p. 63.)
If the amount of read data exceeds the buffer capacity, the N-400 sends back
the “BUFFER OVERFLOW” error code to the host computer (
➮ see p. 63), and
clears all data stored in the transmission buffer.
In this case, the N-400 stops its operation. The N-400’s operation restarts when
the “PASS” command is sent to the N-400 in response to the “OVER” code.
N-400 • • •
Read data
N-400 • • •
Read data
Response (PASS,RTRY)