Modbus Communication Protocol - Honeywell XYR 5000 Series User Manual

Honeywell Industrial Wireless
6.2: Modbus Communication
Protocol
NOTE
This
device supports Modbus RTU (Binary)
communications. Note that the ASC-II transmis-
sion mode is not supported.
16 Rev. 3
11/04
The Base Radio connects to the Host (Master) system using Modbus over
a serial RS-485 line. The Base Radio supports Modbus RTU transmission
mode at baud rates of 9600, 19200, 38400, 57600, or 115200 baud with
even, odd, or no parity and 8 data bits. One stop bit is used if even or odd
parity is selected and two stop bits are used if the no parity option is se-
lected to fill out the character frame to a full 11-bit character. Unless
modified by the user, default values of 19200 baud, 8 data bits, even par-
ity, and one stop bit are used.
The Base Radio is always located at the device ID selected by the DEV
ID menu item. Transmitters can be configured to either be assigned to an
individual Modbus device ID or to holding registers within the Base Radio
device ID through the appropriate selection in the MODMAP menu item.
There are two MODMAP modes available: DEVMODE and REG-
MODE.
If the device ID mapping mode (DEVMODE) is selected, a Transmitter's
equivalent Modbus device ID is the Base Radio's device ID plus the
Transmitter's RF ID. For example, if the Base Radio's device ID was 10
and a Transmitter's RF ID was 5, the Transmitter would be accessed un-
der Modbus device ID 15. Using the device ID mapping mode adjusts the
upper limit of the Base Radio's device ID to 247 minus the number of
Transmitters on the RF network. For instance, if 5 Transmitters were on
the Base Radio's network, the maximum Modbus device ID would be
242.
If the register-mapping mode (REGMODE) is selected, a Transmitter's
data may be accessed with the Modbus Read Holding Register command
(03) using the Base Radio's device ID. The Base Radio uses register ad-
dresses 1 through 10 with each subsequent group of 10 registers used by a
Transmitter.
The RF online/offline status of a Transmitter can be determined through a
number of different sources. In the Base Radio holding registers, a count
of the current number of online Transmitters can be found at address
00004. Also the individual online/offline status of each Transmitter is
stored in the Base Radio holding registers at addresses 00005, 00006,
00007, and 00008. These registers are bit field variables with each bit of
the 16-bit number representing the status of a Transmitter. If the bit is set,
the corresponding Transmitter is online. If the bit is cleared, the corre-
sponding Transmitter is offline.
In the Transmitter holding registers, bit 1 in the Transmitter & Sensor
Status holding register holds the online/offline status of the particular de-
vice. Any Transmitter that is currently offline will return NaN (Not a
Number) when queried for its primary or secondary measurement value.
Note that if a Transmitter is online and is a single measurement device
type, NaN will also be returned for the Secondary Sensor Value as the
measurement does not exist in these devices.
User Manual
Wireless Base Radio