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Checksum: An optional two character checksum denoted [CS] can be included immediately before the
terminating (CR). The purpose of the checksum is to help the PC and devices detect the communication errors
that have corrupted the command strings. When the checksum is enabled all commands from the PC to the
devices and all responses from the devices must contain a valid checksum otherwise the data is discarded.
When the checksum is enabled, commands sent without a valid checksum will be ignored by the devices and
the device will not respond to the host PC. By default the checksum is turned off. To turn checksum on, you
must configure the device via its webpage using a browser.
In the following sections of this chapter, those parts of the command string in lower case are parameters that
the user must enter. Those parts of the command string in capitals, or which are numbers or punctuation
symbols, are to be used literally in the command without replacement by the user.
Additionally, any parts of the command string that are in square brackets are optional. The checksum is an
example of this as it is only required when the checksum is enabled in the firmware of the device.
Example Commands: Assuming that the checksum has not been turned on by the user, one of the simplest
commands is:
$aaM(CR)
This command reads the status of the digital input port. Assuming the ED devices address is 01, that is aa=01,
then the command the user would issue would be:
$01M(CR)
The response to this command from an ED-549 device at factory default settings would be:
!01ED-549(CR)
Response Format
The response received from the device will depend on the ASCII command that has been sent. The response
for each command is detailed in the Command List Section.
* Only applicable for certain commands that return data.
** Optional parameter for the command.
Prefix or Delimiter: Each ASCII response starts with a single character prefix or delimiter. The prefix will be one
of the following three characters:-
Greater than sign, ASCII value hex 0x3E
Exclamation sign, ASCII value hex 0x21
Question mark sign, ASCII 0x3F
Address: The address is a two character field giving the hexadecimal address of the device (00-FF). The default
address is 01. The address field is written as aa in the examples that follow.
Data: The data being sent from the device in response to the command sent.
Checksum: Optional 2 character checksum.
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