Prevac MG15 - Type of Data Used in Communication; Erros Codes

COMMUNICATION MULTI GAUGE CONTROLLER
continued from previous page
Error
code
Error type Description
0x06 Busy /
Message
discarded
The server (Slave) is busy for long time with processing the pro-
gramme commands. The Client (Master) should try again to send the
message later, when the server (Slave) is free.
0x07 Not ac-
knowledge
The response of the device inquired when the required action cannot
be executed.
0x0A Network
path un-
available
Applies to network gates. It indicates that the network gate cannot
allocate an internal communication path from the input port to the
output port to execute the command.
0x0B No response Applies to network gates. This means that no response has been re-
ceived from the target device. It usually means that the device is not
present in the network.
Table 6.9: Erros codes
6.4.7 TYPE OF DATA USED IN COMMUNICATION
One of the main limitations of the Modbus protocol is the fact that the device memory is visible
as a variable 16-bit integral numbers table. In most cases it is suficient, because scaling to the
appropriate value without losing precision can be used. In fact it has a disadvantage consisting in
the fact that the scaling factor must be known for the devices at both ends of the communication
link.
The next problem are variables, for which 16-bit representation is not suficient, e.g. value of vac-
uum. To solve these problem, different types of variables have been implemented in the MG15,
enabling the full resolution of data.
The most precise data type is 32-bit loat in the ”IEEE-754” standard. This format is written in the
memory as two consecutive words (4 bytes) in the order: “MSB irst”. The rules determining the
organisation of data in two consecutive words depends on the type of a given parameter.
Other data types used in the Modbus protocol variables:
• Enumerating parameters are parameters, which have their own text representation in the
user interface, e.g.: “Type of gauge:” - ”CTR90, TTR91, TTR211,...”, etc.
• Parameters of ”bool” type are parameters which may be ”0” or ”1”. These parameters are
described in the table as “bool”.
• Parameters of ”integer” type are integral parameters, without decimal points. They include
parameters such as “Degassing power” or “Sensitivity”. They can be 8- or 16-bit parameters
and are marked in the table as ”uint8” or ”uint16” for integer numbers without sign and ”int8”
or ”int16” for integer numbers with sign.
• Parameters of ”loat” type are parameters with a decimal point. These are parameters such as
“Vacuum value” or “Setpoint” settings. These parameters are marked in the table as ”loat32”
and their writing is compatible with the 4-bytes ”IEEE-754” standard.
Page 98 User manual rev. 03