Sanyo 550 instruction manual Packet Flow Summary, Functional Layer Definition, Types of Packets

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 takeplace 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).

7.3.4FUNCTIONAL LAYER DEFINITION

Types of Packets
Description	CONTROLLER CONFIGURATION REQUEST
Type	Command
Source	master
Header	128
Data Block	No

This packet instructs the Controller to reply with information as to its type and configuration.

Description	CONTROLLER CONFIGURATION
Type	Reply
Source	Controller
Header	128
Data Block	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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