Modbus Overview; Modbus Point/Numbering Structure; Analog Register - Viessmann Vitogate 300 Supplementary Documentation

Modbus Overview

Modbus Overview
The VS Address is a number that Viessmann uses
as an internal point in each control to define the
points that are able to be taken from the device. It
is this point that is selected when you configure
the gateway for the points that you are looking for
on either the Modbus or BACnet side of the BMS.

Modbus Point/Numbering Structure

It must be understood that there are some
points in the Cascade/Lead boiler controls
which are not available in lag boiler controls.
However points between lag boilers will
typically be consistent.
When register values are known, it is possible to
add a value of 500, to calculate the next control
assuming that address 77 values are consecutive.
Example:
Boiler 2 IN523 is Flue Gas Temperature
Boiler 3 IN1023 is Flue Gas Temperature
Boiler 4 IN 1523 is Flue Gas Temperature
.
.
.
Boiler 8 IN3523 is Flue Gas Temperature
Binary Information
CO=coil which is a Boolean/Digital point that is
read/writeable
ST=Status is a Boolean/Digital point that is only
readable
Analog Information
IN=analog input register which is a read only
integer 16bit
HO=Holding is an analog output point which is
read/writeable
Binary Register
Coils: discrete output coils (read-write
Boolean, 1 Bit) Range/Register 1 – 9999
Status: discrete input coils (read-only
Boolean, 1 Bit) Range/Register 10001 - 19999

Analog Register

Input: registers analog input register (read-
only integer, 16 Bit) Range/Register 30001 –
39999
Holding: registers analog output holding
register (read-write integer, 16 Bit) Range/
Register 40001 – 49999
The allocation of bits or registers have what
meaning can only be established in the form of a
data point list. Additional information such as the
name of the information unit, limits or min / max
information cannot be determined.
The 16-bit data registers may need to be scaled or
converted. Vitogate used formats:
• Integer unsigned and signed (u - unsigned, s -
signed)
• a factor of 10 (one decimal place) (ut, unsigned
tenth, st - signed tenth)
• a factor of 100 (two decimal places) (uh,
unsigned hundredths, sh - signed hundredths)
• Factor 1000 (three decimal places) (order,
unsigned mega, sm - signed mega)
The conversion must be done on the master side
(the client).
Supported function codes
In order to read or write the data from Vitogate
following MODBUS function codes are supported:
§ 01 (0x01) Read Coils
§ 02 (0x02) Read Discrete Inputs
§ 03 (0x03) Read Holding Registers
§ 04 (0x04) Read Input Registers
§ 05 (0x05) Write Single Coil
§ 06 (0x06) Write Single Register
u: Numerical value without prefix is unsigned,
cannot have negative values
s: Numerical value with prefix can have a negative
value
t: Numerical value is one tenth of the value
displayed
h: Numerical value is one hundredth of the value
displayed
m: Numerical value is one thousandth of the value
displayed
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