Timing Constraints; Ascii Hex Protocol Examples - Hydronix Hydro-View HV02 User Manual

ASCII HEX MODE
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)
A typical response to this frame might be...
ASCII Character code (in hex)
78
HYDRO-VIEW USER GUIDE D0022 REV 1.06
Description
02 STX
30 Station number 03
33
30 Request code 01 - read moisture
31
30 Material number 05
35
30 Checksum 07
37
03 ETX
Description
02 STX
38 Station number 83 (slave reply sets the top bit!)
33
30 Request code 01 - read moisture
31
41 NOW value in hexadecimal is 02A3. Converting
33 this to decimal gives 675 or 6.75%.
30
32
37 AVERAGE value in hexadecimal is 0271.
31 Converting this to decimal gives 625 or 6.25%.
30
32
31 Status flags indicating...
31 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 Checksum 7E
45
03 ETX