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An Explanation of Each Field is as Follows:
Framing Character A "!" character is used to signal the start of a new message. This character is only ever
transmitted by the host, for framing purposes
Station Address A three-digit ASCII decimal number (0-999), determining which slave device(s) the command is
intended for. All three digits must be sent. In the case of the DSCUSB this will always be 001
Separator always present. As no checksum or message verification technique is used, slaves use this as an extra
check on message validity
Command Identifier. Up to 4 alpha-numeric characters, case insensitive, giving the name of the required
command.
Access Code. Defines what sort of response is expected :–
'=' means write data is expected to follow
'?' means the host is expecting to receive read data back
<CR> (i.e. nothing more before end) means the command is an action type (execute)
End of frame. A <CR> is always present to indicate the end of the message
Response Message Formats
There are Three Possible Types of Response: acknowledge (ACK), acknowledge with data (for a read), and not-
acknowledge (NAK)
ACK-with-data is a decimal number, followed by <CR>. This confirms a read and returns the data value.
NAK is an '?' <CR> sequence. The device rejected the command.
There are several possible reasons for a NAK response
Command identifier not recognised.
Badly formatted command: Missing command identifier, unrecognised access-code character, or unexpected
character somewhere else.
Access attempted not supported by this command.
So a successful response example would be:
123.456<CR>
Software Command Reference
Serial Port Settings
The communications settings for the virtual COM port are:
115200 baudrate
8 data bits
1 stop bit
No parity
NOTES:
From receipt of the host's terminating <CR> to a response from the device (if any) will be at most 50mS. After
this, it can be assumed there is no response.
Mantracourt Electronics Limited - DSCUSB Advanced Manual
18
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