Specifications

Halogen Gas Monitor – Multi Zone
50 Instruction 3015-5074
HGM-MZs. If it is not, the message is not passed through. The HGM-RD does not make any modifications to
MODBUS messages. It simply passes the query through to the HGM-MZ, and passes the response back to
the MODBUS master. In other words, it allows the HGM-MZs to be logically connected to the MODBUS
network, when physically they are connected to the local HGM-RD network. It is very important
to understand
that the HGM-RD will only pass messages through to the HGM-MZ when the HGM-RD is either in the
“SYSTEM” screen or the “ZONE VIEW” screen. If the HGM-RD is in any other screen
, it will return a
MODBUS “busy” exception response (exception code 06).
All HGM-RD screens, except the SYSTEM and ZONE VIEW screens, have a 10 minute timeout interval. After
This, the screen will return to the SYSTEM or ZONE VIEW screen, depending on which one was last
displayed. The HGM-RD may also be password protected so that a password entry is required in order to
view screens other than the SYSTEM or ZONE VIEW screen.
Key Comm Protocol Parameters
MODBUS Mode: RTU only
HGM-MZ Baud Rate: Default is 19,200. Programmable as defined in System data register
Parity: No Parity
Stop Bits: Default is 1. Can be set for 2 via System data register
Maximum Response Time:
4000mS when directly accessing the HGM-MZ
8,000mS when accessing the HGM-MZ through the HGM-RD.
Error Checking: CRC per MODBUS specifications
NOTE: All data
sent out from the HGM-MZ is in “little endian” byte order (Least significant byte followed by
most significant byte). This should be taken into account if the master that process the data is a “big endian”
type. Non-data information (starting address, number of points, etc.) follows normal MODBUS protocol, which
is Big Endian.