4.4 Internal Local Registers (Slave ID 199) for the DXM700, DXM1000,
and DXM1200
The main storage elements for the DXM700 are its local registers, which can store 4-byte values that result from register
mapping, action rules, or ScriptBasic commands.
Local registers updated from Modbus transactions are restricted to a16-bit data value to follow standard Modbus holding
register definition.
The local registers defined in action rules must all be within the same register group. For example, an action rule cannot have
inputs from an integer group with the result register defined as a floating point register. To move between integers and floats,
use the Register Copy Rule.
•
Local registers 1–850 and 5001–7000 are 32-bit integer registers
•
Local registers 851–900 and 7001–8000 are non-volatile 32-bit integer registers
•
Local registers 901-1000 are reserved for internal use
•
Local registers 1001–5000 are floating point format numbers, each address stores half of a floating point number; for
example, registers 1001 and 1002 store the first full 32-bit floating point number
•
Local registers 10000 and higher are read only virtual registers; virtual registers collect various system-level data
Table 13: Modbus registers for internal local registers (Modbus slave ID 199)
Local Registers
Type
Description
1–845
32-bit integer
Local data registers
846–849
32-bit integer
Reset, Constant, Timer
851–900
32-bit non-volatile integer
Data flash, non-volatile
901–1000
Reserved for internal use
1001–5000
Floating point
Floating point registers, local data registers
5001–7000
32-bit integer
Local data registers
7001–8000
32-bit non-volatile integer
Data flash, non-volatile
> 10000
Read only virtual registers, system-level data
Local registers 1–850 and 5001–7000
(Internal Processor Memory, 32-bit, Unsigned)—The local registers are the main
global pool of registers. Local registers are used as basic storage registers and as the common data exchange mechanism.
External Modbus device registers can be read into the local registers or written from the local registers. The DXM700, as a
Modbus master device or a Modbus slave device, exchanges data using the local registers. Modbus over Ethernet (Modbus/
TCP) uses the local registers as the accessible register data.
Local registers 851–900 and 7001–8000
(Data Flash, Non-volatile, 32-bit, Unsigned)—The top 50 local registers are
special non-volatile registers. The registers can store constants or calibration type data that must be maintained when power
is turned off. This register data is stored in a data flash component that has a limited write capability of 100,000 cycles, so
these registers should not be used as common memory registers that change frequently.
Local registers 1001–5000
— These local registers are paired together to store a 32-bit IEEE floating point format number in
big endian format. Registers 1001 [31:16], 1002 [15:0] store the first floating point value; registers 1003, 1004 store the
second floating point number. There are a total of 2000 floating point values; they are addressed as two 16-bit pieces to
accommodate the Modbus protocol. Use these registers when reading/writing external devices that require Modbus registers
in floating point format. Since Modbus transactions are 16-bits, the protocol requires two registers to form a 32-bit floating
point number.
Virtual registers
—The DXM700 has a small pool of virtual registers that show internal variables of the main processor.
Some register values will be dependent upon the configuration settings of the DXM700. Do not use
Read Rules
to move
virtual local registers data into local registers. Use the
Action Rule
>
Register Copy
function to move virtual local registers
into local registers space (1–850).
Table 14: Modbus registers for virtual registers
Registers
Definition
10001
GPS latitude direction (N, S, E, W)
GPS Coordinate Data if the DXM is configured to read an external GPS unit.
10002
GPS latitude
10003
GPS longitude direction (N, S, E, W)
10004
GPS longitude
Sure Cross
®
DXM700-Bx Wireless Controller
26
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