100/180 mm PAPERLESS GRAPHIC RECORDER: USER GUIDE
HA028910
Issue 13 Sep 16
User Guide
Page 282
EXCEPTION CODES
MODBUS TCP provides reserved codes used for exceptions. These codes provide error information
relating to failed requests. Exceptions are signalled by hex 80 being added to the function code of the
request, followed by one of the codes listed in table 8.2.1b, below.
An invalid function code was received
Illegal Function
01
Illegal Data Value
Slave Device Failure
Gateway path unavailable
Gateway target device
failed to respond
An invalid data value was received
An unrecoverable error occurred in the recorder
Gateway misconfigured or overloaded.
Device not present on the network
03
04
0A
0B
Code
MODBUS definition
Description (see Modbus specification for full details)
An invalid data address was received
Illegal Data Address
02
Hex
Dec
01
02
03
04
10
11
Illegal Sub Function
An invalid sub function was received.
09
09
Table 8.2.1b Exception codes
8.2.2 Data types
The following data types are supported:
1 2’s complement signed 16-bit analogue values with implied decimal point. The decimal point posi-
tion must be confi gured in both the recorder and the host computer.
2 2’s complement, 16, 32 and 64 bit signed integers.
3 16-bit unsigned integer values.
4 32 bit IEEE Floating point values.
5 Strings of limited size, can be transferred across Modbus TCP in ASCII format using a single non-mul-
tiplexed set of consecutive registers.
DATA ENCODING
MODBUS uses what is called a ‘Big endian’ representation for addresses and data items. This means that when
a numerical quantity larger than a single byte is transmitted, the most signifi cant byte is sent fi rst. For example
a 32-bit hex value of 12345678 would be transmitted as 12, followed by 34, followed by 56 and fi nally 78.
8.2.3 Invalid multiple register writes
When a recorder receives a multi-register write request, it is possible that one or more requests will be re-
jected. Under such a circumstance, the recorder will accept all valid write requests and ignore any invalid
writes. No error response is produced.
8.2.4
Security
The recorder has a local fi le in which are stored all users’ login information, as set up in Security/Access
confi guration (
section 4.4
) it must then supply the correct Username and Password. Should a host fail to
login after three attempts, the recorder will terminate the connection.
This MODBUS security function can be enabled/disabled in the Operator/Confi g/Instrument menu (
sec-
tion 4.3.1
).
Note: Modbus Security must be disabled in order for Modbus communications to be established.
Once the Master is communicating with the Slave, Modbus security can be re-enabled, providing
that the master has the correct remote user name and password data for the relevant slave. If this
information is missing, all read/write requests will be ignored by the slave.
