BMT 964 - Function Code 1 - Read Single Coil

OZONE ANALYZER BMT 964 Manual, Rev. 04/2021
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col exception 4 is used, because the standard does not define an exception, that will convey to the
master the use of an out-of-range system parameter. There is no "unrecoverable error". Excep-
tion 4 merely means that the request was rejected and nothing was changed.
The BMT 964 supports a subset of the standard MODBUS RTU function codes:
Function Code Name Usage
1 Read Single Coil Read binary data, e.g. alarms
3 Read Holding Registers Read numeric data, e.g. concentration
5 Write Single Coil Write binary data, e.g. zero command
8 Diagnostics Check communication quality
16 (10h) Write multiple registers Write numeric data, e.g. alarm limits
The following section describes these function codes and their use in detail. The following tables
contain register addresses referring to the MODBUS data model (starting with 1), not the actual
content of the data stream (where address space starts with 0).
Caution: Care has to be taken that the MODBUS master does not reconfigure the BMT 964 in an
endless loop. The internal non-volatile memory will only tolerate a limited (1,000,000) number of
write cycles. Reading commands can be used infinitely.
Function Code 1 – Read Single Coil
This code is used to request binary status information from the instrument. The query consists of
a start coil number (first register to receive data from) and the quantity of bits to read. The first
bit of the first byte of the response contains data from the start coil number. Data from the other
coils fill up the bits of the first and subsequent bytes in low to high order. Bits not used in the last
byte will be padded with zero. Status is indicated as 1 = ON, 0 = OFF.
Start Coil Description
1 Low Alarm
2 High Alarm
3 Low Alarm Enabled
4 Low Alarm Latched
5 High Alarm Enabled
6 High Alarm Latched
7 Lamp Low Warning
8 Lamp Low Error
9 Lamp Off Error
10 Lamp High Error
11 Cuvette Dirty Warning
12 Cuvette Dirty Error
13 Overrange Error
14 Overpressure Error
15 EEPROM Error
16 Zeroing
17 Warming Up