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The Controller has buffered interrupt driven communications. This ensures that
Command Packets from the master cannot be lost even if the Controller's processor is
preoccupied with another task. If the Controller's processor is preoccupied, however
(e.g. accessing the disk or repainting an area of the screen), the Controller will not issue
the Reply Packet immediately.
The master should allow the Controller up to 12 seconds to reply. If no reply is received
12 seconds after the Command Packet was issued, it can be assumed that
communications have been lost with that Controller (e.g. noise caused Command Packet
to become corrupted, Controller switched off or disconnected, etc).
It is important that the master should wait for a reply from the Controller (up to the 12
second time-out) before issuing any more Command Packets. If this precaution is not
observed, a packet clash could take place on the RS485 bus. Even if the master software
is only intended to run in a single Controller configuration (using RS232), observing
this precaution will ensure compatibility with the RS485 configuration.
Packet Flow Summary
master transmits Command Packet to Controller,
if the Controller fails to receive the packet in full, or one of the check-
sums is wrong, the packet is ignored & the Controller takes no further ac-
tion. In this case, the master would realise that the packet was lost after
the time-out period, & would be able to re-transmit the Command Packet
if the Controller receives a correct Command Packet from the master, it
acts on the command and issues the appropriate Reply Packet as soon as
it can (usually within Is, but always within 12s).
7.3.4 FUNCTIONAL LAYER DEFINITION
Types of Packets
Description
Type
Source
Header
Data Block
CONTROLLER CONFIGURATION REQUEST
Command
master
128
No
This packet instructs the Controller to reply with information as to its type and
configuration.
Description
Type
Source
Header
Data Block
CONTROLLER CONFIGURATION
Reply
Controller
128
22 bytes
The data bytes of the Controller Configuration Reply are as follows (in the order in
which they appear in the data block):
4 bytes: Controller type string, (2000 for Format 550)
4 bytes: Controller software version string (lOOths with leading zeros),
eg "0144" represents V1.44.
1 bytes: humidity enabled. (l=enabled, 0=temperature only chamber)
1 byte: third variable enabled. (l=enabled; 0=no third variable);
normally "0" for Genus chambers.
12 bytes: Third Variable description string; eg "Light".
This string contains trailing spaces to pad to 12 characters.
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