Honeywell Midas-M, User Manual

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A Modbus/TCP Interface
The Midas-M gas detector can report concentration information in a variety of formats
including relay contact closure, an analog 4-20 mA loop, Ethernet/ IP/HTML web pages and via
the Modbus/TCP networking protocol. This section defines the format of data in Modbus/TCP
registers. More information about Modbus/TCP can be obtained from www. modbus.org.
The Midas-M is a Modbus/TCP “server” as defined in the MODBUS Application Protocol
Specification V1.0 . It supports command 03 (“read holding registers”) for registers 40001 to
40122 as listed in the following table.
The Midas-M reports floating-point concentration numbers in little-endian or Intel format. This
is scaled in units of ppm for gasses which have display units of ppm or ppb. For other display
units the concentration is scaled directly in display units. This applies to registers Gas
Concentration and Alarm Threshold.
The Midas-M fills 122 Modbus/TCP holding registers as listed in Table 1. The Monitoring Status
register is a concise summary of Midas-M status. The other registers provide more complete
information.
Midas-M Modus Register Map
Midas-M Modbus Register Map : Register 40001 is mapped with base address (zero)
(If channel is disabled, channel information is 0).
ModBus
Register
Number
Information R/W
Data
Type
Data
Size
(Byte)
Description Note
Holding Register
Device Status
40001 Reserved for
future
expansion R 2
Midas-M 86 User Manual