Master Data Telegram
The Master Data Telegram is transmitted by the master
after the Amplifier Telegram. It consists of one long
message, with space allocated for each drive on the
ring, as shown. All drives have previously been instructed
where their data is located within the MDT. As the MDT
is received by a drive, it “fast forwards” to the starting
location for its information and retrieves it.
Structure
of the Master Data Telegram
The Master Data Telegram is similar
to the Amplifier Telegram, except that the data field
includes a record for each drive on the ring. Like
the AT, each data record in the MDT consists of a
fixed and variable data portion in three fields:
- Control field – This 8-bit field enables or disables
the drive and configures the service channel.
- Master service info – Implements setup parameters
and special functions, such as homing, probing and
coordinate offsets.
- Operation data for drive xx -- This field contains
a series of IDNs (idents) specifying real-time operating
data and drive commands for the addressed drive.
The chosen idents depend on the application.
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