Control Techniques M'Ax 403, Руководство пользователя

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88
M’Ax User Guide
Issue Number: 4
Message sequence
A typical message sequence is as follows:
1.
The host enquires the value of a parameter in a Drive.
2. The Drive sends the value.
3. The host sends a command to the Drive to change the value of the
parameter.
4. The Drive sends an acknowledgement that the parameter value has
been changed.
Control codes
Commands, requests and responses can contain the following codes:
EOT
(Reset)
From the host: Instructs a Drive to receive a message
From a Drive: Indicates that an addressed parameter does not exist
ASCII code: 04
Keys: Ctrl D
STX
(Start of text)
From the host: Start of a command
From a Drive: Start of a reply
ASCII code: 02
Keys: Ctrl B
ETX
(End of text)
From the host: End of a command
From a Drive: End of a reply
ASCII code: 03
Keys: Ctrl C
ENQ
(Enquiry)
From the host: Instructs a Drive to reply with the value of a specified
parameter
ASCII code: 05
Keys: Ctrl E
ACK
(Acknowledge)
From the host: Instructs a Drive to reply with the value of the next
parameter in the menu
From a Drive: Last command from host has been accepted and
performed
ASCII code: 06
Keys: Ctrl E
NAK
(Negative acknowledge)
From the host: Instructs a Drive to reply again with the value of a
parameter
From a Drive: Last message from host was rejected because of any
of the following:
•
Invalid message structure
• Specified parameter does not exist
• Data too long or out of range
• Attempting to edit a read-only parameter
• BCC incorrect (message corrupted)
ASCII code: 21
Keys: Ctrl U
BS
(Backspace)
From the host: Instructs a Drive to reply with the value of the
previous parameter in the menu
ASCII code: 08
Keys: Ctrl H
Addressing the devices
Addressing device(s) is performed by specifying an address number
immediately after the start bit in a message. This address number is the
same as the address of the device but modified by repeating each of the
address digits.
To address an individual device, for example unit
6 in group 4 , which has
the address 4.6 , the address used must be 4466 .
To address a group of devices, for example group 4 , the address used
must be 4400 .
To address all devices, the address used must be 0000 . (eg. to start all
the Drives in a system at the same time).
When group addressing is used, the Drives will not transmit an
acknowledgement since simultaneous transmissions will produce
meaningless data.
Specifying a parameter
Commands and enquiries require a parameter number to be specified
after the address in a message. Four digits must always be used
(eg.
0000 , 1101 , 0103 ).
Specifying a value
Values are expressed as decimal numbers. The number of characters
used for conveying a value depends on the value itself.
One of the following characters must be preceed the value:
Space (ASCII 32)
+
–
For example, this allows the value –1 to be transmitted.
Checking for data corruption
Messages that carry data are terminated by a block checksum (BCC)
character. This is described in Block checksum later in this chapter.
C.6 Message structure
Key
Request the value of a parameter (read-command)
Host to Drive
Example
Group 4, Unit 6
Parameter
1.17
Host sends: EOT 4466 0117 ENQ
Reply to a request for a parameter value
Drive to host
Example
Value of parameter 1.17 is –4500
Drive sends: STX 0117 –4500 ETX (
G Group number
U Unit number
m1, m2 Menu number
p1, p2 Parameter number
v1...vn Parameter value (variable number of bits)
EOT G G U U m1 m3 p1 p2 ENQ
STX m1 m2 p1 p2 v1 ... vn ETX BCC