LubriMist
®
Model IVT
Oil Mist Generating System
Installation and Operating Manual
Page 133
of 256
Figure 7
Remember;
the Hex Addresses can only be read in a string (Beginning, Middle or End).
Warning;
As in section (1), when placing values in the Address (HEX) and Length boxes in the Modscan
screen, the values cannot exceed their specified limits for each function code.
Function Codes
01 Coil Status----—----Address (HEX) and Length cannot exceed 11 or Modscan will stop
receiving data and lock on to the previous values.
02 Input Status --------- Address (HEX) and Length cannot exceed 11 or Modscan will stop
receiving data and lock on to the previous values
03 Holding Register---- Address (HEX) and Length cannot exceed 25 or Modscan will stop
receiving data and lock on to the previous values
04 Input Register-------- Address (HEX) and Length cannot exceed 14 or Modscan will stop
receiving data and lock on to the previous values
General Information
All Modbus transmitted values consist of one or more 16-bit binary “words”. These are used in
various ways to represent the particular item or value as determined by the message context.
The format used for Coil Status or Input Status is explained first followed by that for Holding
Registers or Input Registers.
Coil Status or Input Status is transmitted in what is sometimes called a “packed-bit” format. This
refers to the fact that the individual status values are “packed” into the individual bits of a larger
16-bit data word. Specifically, the individual bits are arranged in increasing numeric order,
according to their data address, and starting at bit number zero.
High byte of 16-bit value
Low byte of 16-bit value
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
S
15
S
14
S
13
S
12
S
11
S
10
S
9
S
8
S
7
S
6
S
5
S
4
S
3
S
2
S
1
S
0
S
0
= Status bit transmitted with lowest address number
…
S
15
= Status bit transmitted with highest address number
Note that if a particular transmission request involves less than 16 individual status
addresses, then the upper bits will be unused. The Modbus specification allows for many
more than 16 status bits to be transmitted at one time using multiple 16-bit words but the
IVT Oil Mist Generator has no need to ever transmit more than ten (10) at one time.
Holding Registers or Input Registers are transmitted as 16-bit words with one analog
numeric value per word. The format used is what is referred to as “twos-complement”
integer form. Each 16-bit value is treated as a 15-bit integer with a 1-bit sign. This
allows for the transmission of negative numbers for those registers that may need to
represent values below zero. Fifteen integer bits plus sign allow for numeric values in the
range –32768 to +32767
.
High byte of 16-bit value
Low byte of 16-bit value
