Data transfer
AS-i messages
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Lenze · Decentralised frequency inverter 8400 motec (AS-Interface option) · EDS84DMOTASI EN 5.0 - 02/2019
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7
Data transfer
AS-Interface transmits parameter data, configuration data, diagnostic data, alarm messages and
process data between the host (master) and the inverters (slaves) that are part of the fieldbus. The
data are transmitted via corresponding communication channels as a function of their time-critical
response.
The bus access method of the AS-Interface is a master-slave method with cyclic polling.
• The master transmits a frame (master call) with a specific slave address.
• The slave triggered with this address responds within the allowed time (acknowledgement of
the message).
• When the response has been received correctly from the master, the message is deemed to be
transmitted successfully.
• If the master does not receive any response or the response cannot be decoded without errors
for the master, the frame can be repeated.
7.1
AS-i messages
An AS-i message consists of ... a master call, a short pause, a slave response, and a short pause again.
• All master calls have a length of 14 bit times (1 bit time = 6
μ
s).
• All slave responses have a length of 7 bit times.
• The 1st pause has a typical duration of 16
μ
s (synchronised slave) and must not be longer than
the expected slave response.
If during this time the master does not receive the start of a slave response, no response will
arrive anymore. Now the master may start with the next call.
• At the end of the slave response, there is a short pause again with a typical duration of approx.
9 … 12
μ
s.
The master needs this time to check the slave response and decide what should happen next
(repeat the transmitted call or continue with the next call).
Broadcast call of the master
An exception to this message structure is a broadcast request of the master. A broadcast
transmission corresponds to broadcasting to all nodes (simultaneous transmission from the master
to all slaves). It can only be effected in one direction. Broadcast transmissions cannot be
acknowledged. Hence, it is not ensured that all slaves have received the message correctly.
Master call
Pause 1
Slave response
Pause 2
14 bits
7 bits
84
μ
s
16
μ
s
42
μ
s
9 ... 12
μ
s
151 ... 154
μ
s
