Host Computer
Command
Completion of command transmission
Command retransmission 
(only twice)
Abnormal reception
Normal reception 
ACK
Other than ACK
Notes:
Scanner
Abnormal reception
Normal reception
ACK
Other than ACK 
$Command processing
$Operation
Response
Response transmission end
Response retransmission (only
1.Abnormal reception means that a parity error, flaming error, overrun error, or count error has occurred.
2.Command or response transmission is retried only twice.
3.Upon reception, a command or response is checked for transmission errors. When the check result has no problem, ACK is returned immediately to the originating source. When the check result has problem, data other than ACK is returned after all data has been received.
4.The originating source of the command/response monitors the response from the receiving side. ACK indicates that command/response transmission is completed. Data other than ACK causes the command/response to be transmitted again. The transmission is retried only twice. After that, the scanner waits for a new command.
5.Response data such as ACK must be returned to the originating source within 0.5 second.
6.The interval between words in the data steam must be no more than 10 ms.
Figure 6.1 Basic command/response sequence
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