44
MODBUS-GW Installation and Operation Manual —
P/N LS10015-000NF-E:C2 4/30/2019
Appendix B Exception Responses
If a Modbus master device sends an invalid command or attempts to read an invalid holding register, an exception response is generated.
The exception response follows the standard packet format. The high order bit of the function code in an exception response is 1. The
data field of an exception response contains the exception error code.
describes the exception codes sup-
ported and the possible causes.
Table B.1 Exception Codes
Exception Code
Conditions
Exception Name
0x01
• Protocol Identifier in Modbus packet does not match
Modbus protocol. Protocol Identifier in Modbus should
always be “0”.
• Function code sent by the client is not supported by the
MODBUS-GW or the FACP.
• A Control command was sent to the gateway. Contact
customer service.
Illegal function
0x02
• Register address range specified by the client is not
supported by the FACP.
• Register address range requested is valid but the device
(e.g. Detector, Module, Zone, etc.) is not present in the
specified FACP.
• Analog Value is requested from a register which is not
associated with a 4–20 mA device.
Illegal data address
0x03
• Number of registers requested exceeds the maximum
allowed limit. The maximum number of registers that a
client can read at one time is 100. The exception to this is
for analog values where the maximum number of
registers a client can read at one time is 10.
• Invalid Data written to the register when sending
commands.
Illegal data value
0x0A
Unit ID specified in the request packet is not configured for
monitoring.
Gateway path failed
0x0B
FACP is off line or there is a communication problem on the
panel and/or NFN.
Gateway target failed
