Mindeo FS580, Руководство пользователя

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96
6 SCI transactions
6-1 ACK/NAK handshaking
If ACK/NAK handshaking is enabled, all packeted messages must have a CMD_ACK or CMD_NAK
response, unless the command description states otherwise. This parameter is enabled by default, and
should remain enabled to provide feedback to the host. Raw ASCII data and WAKEUP command do not
use ACK/NAK handshaking since they are not packeted data.
The following samples are to show the importance of ACK/NAK handshaking.
ACK/NAK handshaking
is disabled
Host and scanner fail to communicate:
1) The host sends a PARAM_SEND message to the scanner to
change the baud rate from 9600 to 115200.
2) By some reasons, the scanner fails to interpret the message and
does not implement the changes requested by the host.
3) The host assumes that the parameter changes have occurred and
acts accordingly (i.e. applying the new baud rate at 115200).
4) Communications are lost because the change did not occur on both
sides, since the baud rate for scanner is 9600 and the one for the
host is 115200.
ACK/NAK handshaking
is enabled
Host and scanner communicates successfully:
1) The host sends a PARAM_SEND message to the scanner to
change the baud rate from 9600 to 115200.
2) By some reasons, the scanner cannot interpret the message.
3) The scanner CMD_NAKs the message.
4) The host resends the PARAM_SEND message.
5) The scanner receives the message successfully, responds with
CMD_ACK, and implements parameter changes.