Vaisala HMM105 - Manual (Page 8)

Technical Reference _________________________________________________________________
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HMM105 State Machine
The main and initial state of the HMM105 is Idle, and it will change to
WaitResponse state only when a valid invoke is received. In
WaitResponse state HMM105 expects to see an I 2 C read operation. After
seeing a read operation the HMM105 outputs its response with
ACK/NACK and status signals.
If HMM105 is in WaitResponse state and the master sends a new invoke,
the old response belonging to the old invoke will be lost. When the
master sends the next I 2 C read command, the HMM105 sends it the
response to the latest invoke.
If HMM105 is in Idle state and I 2 C read is sent, HMM105 responds with
a NACK-signal. This tells the master that the data which the master may
have received in same I 2 C read is not valid.
If the HMM105 receives an invalid invoke, it goes to the Idle state. An
invoke message can be invalid because of an unknown command,
erroneous CRC, or invalid message length.
.
1405-073
Figure 2 HMM105 State Machine
Wait
Response
Idle
Valid Invoke
Valid Invoke
Response
NACK
Response
ACK + data
Bad Invoke
Bad Invoke
Response
NACK