Standard Modbus Functions
The Modbus functions supported by the Scanner 3100 are as follows:
Function Code (Hex)
Description
03
Read Holding Registers
10
Preset Multiple Registers
Data Types
Various data types are implemented in the Scanner 3100. The following table lists the formats and the numbers of bytes
and registers associated with each type.
Data Format
Data Type
Byte Count
Register Count
32-bit
Floating Point (FP)
4
1
Unsigned Long (INT32)
4
1
Packed ASCII (String [4])
4
1
16-bit
Floating Point (FP)
4
2
Unsigned Long (INT32)
4
2
Packed ASCII (String [4])
4
2
Enron Record (ER)
—
—
The word ordering for multiple register data types, such as floating-point numbers or long integers, is for the most signif-
icant word to appear first in the message.
Packed ASCII
The Packed ASCII (PA) type contains four bytes that are four unsigned characters. Generally, multiple Packed ASCII
types are arranged consecutively for implementing strings. For example, the Model Number is a string of 16 unsigned
characters that is implemented as four Packed ASCII registers. Here is an example of a model number from the 32-bit in-
ternal Enron Modbus map that contains the string “S3100-G1.”
Register
Hexadecimal
ASCII Characters
105
53 33 31 30
S310
106
30 2d 47 31
0-G1
107
00 00 00 00
<UNUSED>
108
00 00 00 00
<UNUSED>
Unused characters at the end of each string will report 0x00 hexadecimal.
Registers
Each register has an Access type: read-only or read-write, as described below.
Access Type
Description
Read Only (RO)
Register Can Only Be Read
Read/Write (RW)
Register Can Be Read and Written
The registers are grouped into Modbus map blocks according to function. The Scanner 3100 contains the following map
functions.
8
Section 1
Scanner 3100 Modbus Protocol
