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Commands
All commands sent by the CPU5500 central unit start with a ‘%’
sign. The last character is a character which states the end of the
transmission. Just before the end of transmission character, there
are four characters within the command sent to the control panel
which account for the CRC checksum. The CRC checksum is in
uppercase hexadecimal form while all other numbers are in decimal
form. A command sent by the central unit has to be acknowledged.
Therefore the acknowledgement character, ACK, has to be sent to
the central unit. When this ACK character has not been sent back
to the central unit, e.g. due to a communication error, a
retransmission of the last command will follow. The commands
sent by the control panel will also be acknowledged by the central
unit.
The protocol is described as follows:
STX ‘%’ data CRC ETX
With:
STX = start transmit char (0x25 = ‘%’)
ETX = end transmit char (0x0D)
CRC = 16 bit sum of the ASCII characters between STX
and CRC
The acknowledgement char, ACK, has a hexadecimal value of
0x06.
We will adopt a certain notation to explain the messages sent. All
separate entities in a message are represented between curly
brackets. If the contents of such an entity is also between quotes (‘
‘) then this means that this is a literal string. Otherwise it describes
the logical entity. A logical entity will also contain a number
between brackets. This number states how many characters the
entity will exist of. If the subtext
1+
is attached to the entity
between curly brackets, then this means that one or more
occurrences of this entity may occur.
Maybe this notation seems a little hard to comprehend at first, but
some examples should clarify them.
Whenever a microphone of a delegate or the microphone of the
president is activated, then a command is sent to the control panel.
Whenever an active microphone is deactivated, another command
is sent to the control panel. This is also valid when a microphone
goes into request.
The control panel is also able to send commands to the central unit.
You can activate or deactivate a microphone by sending the
microphone number to the central unit.
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