Hydronix Hydro-View HV02, Руководство пользователя

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ASCII HEX MODE
78
HYDRO-VIEW USER GUIDE
D0022
REV 1.06
This is currently the only request frame type supported but meets most application
requirements. Additional facilities will be added at a later date.
Timing constraints
The ASCII-hex protocol requires a communications link of reasonable performance in
particular...
„
A slave station will time out if the request frame does not complete within a period of
0.2 seconds following receipt of the STX character.
„
The slave will normally respond within 0.1 seconds of the request frame being
received. An upper limit on slave response time is set at 1 second, after which the
slave will not begin a transmission. This figure is important to know for multi-drop
systems (i.e. either 2 or 4 wire RS485) to prevent subsequent transmissions from
being ‘jammed’ by a late slave reply.
ASCII Hex protocol examples
Read Moisture request
The following request frame will read the moisture data from station number 3, setting the
material number to 5 in the process.
ASCII Character code (in hex) Description
02 STX
30
33
Station number 03
30
31 Request code 01 - read moisture
30
35 Material number 05
30
37 Checksum 07
03 ETX
A typical response to this frame might be...
ASCII Character code (in hex) Description
02 STX
38
33
Station number 83 (slave reply sets the top bit!)
30
31 Request code 01 - read moisture
41
33
30
32 NOW value in hexadecimal is 02A3. Converting
this to decimal gives 675 or 6.75%.
37
31
30
32 AVERAGE value in hexadecimal is 0271.
Converting this to decimal gives 625 or 6.25%.
31
31 Status flags indicating...
Unit is in average/hold delay period.
Set-point 1 is ON, Set-point 2 is OFF
Material level is OK
Alarm output is OFF
37
45 Checksum 7E
03 ETX