Bosch SSB800 SA - Page 71

SSB 6720892984 (2019/02) US
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K.4 Control register
The control register can be used to gain access to special functions (like writing or controller reset).
Holding register
Access
Description
Automatic
Conversion
Range
R W
99 0063 X X Control register
Bit0: Write Enable.
Bit14: Controller reset.
When no Modbus communication (reading or writing) is sensed for more than 4,0 Seconds the control register will be reset / cleared.
The bits will also be reset when undened bits (i.e. other than bits 0 and 14) are set.
K.4.1 Write Enable
The ‘Write enable’ bit controls if writing to Holding registers is allowed.
‘Write enable’ = 0: Holding registers cannot be written.
‘Write enable’ = 1: Holding registers (that support writing) can be written.
After a write sequence is completed the ‘Write enable’ bit will be automatically cleared. So before each new write action the ‘Write enable’ bit must be set
again. After setting the ‘Write enable’ bit, a write action must be done within max 4 seconds, otherwise the bit is cleared and writing is disabled.

Only enable writing when initiating a write command to a holding register.
Do not send this command when no write is needed to prevent holding registers from being corrupted.
Controller reset
A controller can only be reset when it is in Lockout (lockout error is set).
When the controller is in lockout, it can be reset by setting bit 14 in the control holding register.
Once the reset is executed the bit will automatically be cleared.
K.5 Unit selection
For easier handling of holding registers, the data format can be changed. The data format that is selected will apply for both reading and writing of data.
Holding register
Access
Description
Automatic
Conversion
Range
R W
98 0062 X X Unit selection
Bit0: °C / °F. .
Bit1: Bar / PSI.
Before you can change the unit selection, you must rst enable writing (by setting the ‘Write enabled’ bit in the ‘Control register’).
After this you can set the appropriate bits in the ‘Unit selection’ register.
K.6 Data Types
Modbus communicates using words (the contents of 16bit holding registers).
This means data will be received/send as 16-bit data for each holding register.
Some data types require a higher precision than a whole number (integer), these data types will be multiplied with a factor so the precision is not lost.
When the value for that data type is read it must be divided by the same factor to get the real value.
This also applies to writing the value, then the value must rst be multiplied by the factor before writing it to the Holding register.
Data type Resolution Factor Unit
Temperature xxx.x 10 Degrees Celsius / Fahrenheit (°C / °F)
Voltage xxx.x 10 Volt
Pressure xxx.x 10 Bar / PSI
Flame current (micro amps) xxx.x 10 μA
Percentage xxx.x 10 %