Extended Data Types - Control Techniques unidrive sp Advanced User's Manual

Parameter Keypad and
Parameter x.00
structure display
7.2.9

Extended data types

Standard MODBUS registers are 16bit and the standard mapping maps
a single #X.Y parameter to a single MODBUS register. To support 32bit
data types (integer and float) the MODBUS multiple read and write
services are used to transfer a contiguous array of 16bit registers.
Slave devices typically contain a mixed set of 16bit and 32bit registers.
To permit the master to select the desired 16bit or 32bit access the top
two bits of the register address are used to indicate the selected data
type.
NOTE
The selection is applied for the whole block access.
bit 15 bit 14
TYP1 TYP0
Type select
The 2bit type field selects the data type according to the table below:
Type field Selected data
bits 15-14 type
00 INT16
01 INT32
10 Float32
11 Reserved
If a 32bit data type is selected then the slave uses two consecutive 16bit
MODBUS registers (in 'big endian'). The master must also set the
correct 'number of 16bit registers'.
Example, read #20.1 through #20.4 as 32bit parameters using FC03
from node 8:
Table 7-11 Master request
Byte Value
0 0x08 Slave destination node address
1 0x03 FC03 multiple read
2 0x40
Start register address #20.01
(0x4000 + 201 - 1) = 16584 = 0x40C8
3 0xC8
4 0x00 Number of 16bit registers to read
#20.1 through #20.4 is 4x32bit registers = 8x16bit
5 0x08
registers
6 CRC LSB
CRC
7
MSB
Table 7-12 Slave response
Byte Value
0 0x08 Slave destination node address
1 0x03 FC03 multiple read
Length of data (bytes) = 4x32bit registers =
2 0x10
16bytes
3-6 #20.01 data
7-10 #20.02 data
11-14 #20.03 data
15-18 #20.04 data
19 CRC LSB
20 CRC MSB
366
Parameter Advanced parameter
description format descriptions
bits 0 - 13
Parameter address
X x 100+Y-1
Comments
backward compatible
IEEE794 standard
Not supported on all slaves
Description
Description
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Serial comms
Macros
protocol
Reads when actual parameter type is different from selected
The slave will send the least significant word of a 32 bit parameter if that
parameter is read as part of a 16 bit access.
The slave will sign extent the least significant word if a 16 bit parameter
is accessed as a 32 bit parameter. The number of 16 bit registers must
be even during a 32 bit access.
Example, If #20.1 is a 32 bit parameter with a value of 0x12345678,
#20.2 is a 16 bit parameter with a value of 0xABCD, and #20.2 is a 16 bit
parameter with a value of 0x0123.
Start Number
Read register of 16bit
address registers
#20.1 200 1
#20.1 16584 2
#20.1 16584 1
#20.2 201 1
#20.2 16585 2
#20.3 16586 2
#20.1-
200 2
#20.2
#20.1-
16584 4
#20.2
Electronic Feature look-
Performance
nameplate up table
Response Comments
Standard 16 bit access
to a 32bit register will
0x5678
return low 16bit word of
truncated data
0x12345678 Full 32bit access
Number of words must
Exception 2
be even for 32bit access
Standard 16 bit access
to a 32bit register will
0xABCD
return low 16bit word of
data
32bit access to a 16bit
0xFFFFABCD register will return 32bit
sign extended data
32bit access to a 16bit
0x00000123 register will return 32bit
sign extended data
Standard 16 bit access
0x5678, to a 32bit register will
0xABCD return low 16bit word of
truncated data
0x12345678,
Full 32bit access
0xFFFFABCD
Unidrive SP Advanced User Guide
Issue Number: 7