Honeywell UDC2500 manual Unrestricted Registers, Restrictions on Parameter Numbers in One Message

Modbus RTU Function Codes

File Number

The file number word contains the register number from the register address structure shown in Table 9-1and Table 9-2.Although the register address structure tables indicate up to 13 data registers are available for access, only register address 3 is currently supported.

Register Address

The register address is used to designate the tag ID number for the parameter being accessed. The register address is made up of two bytes—the MSB = 00 always. The LSB contains the RS422 tag ID number. The tag ID numbers represent the parameter’s register address(es). See Section 10 for the tag ID numbers.

Table 9-4 Register Address Format for Function Code 21

Register	Register	Format
Address(es)	Address(es)
(Dec)	(Hex)
001 to 125	0001 to 007D	analog formatted data
		(2 registers – IEEE 32-bit floating point)
128 to 215	0080 to 00D7	integer formatted data
& 255	& 00FF	(2 registers – IEEE 32-bit floating point)

Unrestricted Registers

As mentioned previously, all register data is stored in the EEROM of this instrument with some exceptions. These exceptions were made to allow write access to override information. The registers, which are designated as Override values, are listed below. These registers do not have restrictions on the number of writes.

ID Tag	Register Number	UDC Usage
125	(7Dh)	Computer Setpoint

Restrictions on Parameter Numbers in One Message

The maximum number of writeable parameters per write request is 1.

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