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PanaFlow™ MV80, MV82 & MV84 User’s Manual 109
Chapter 4. Serial Communications
4.2.6.5 Modbus Protocol
The Modbus RTU protocol is supported in this implementation. Supported baud rates are 1200, 2400, 4800, 9600,
19200, 38400, 57600, and 115200. The default baud rate is 19200 baud. Depending upon the Modbus protocol selected,
data is transmitted in 8-bit data frames with even or odd parity and 1 stop bit, or no parity and 2 or 1 (non-standard)
stop bits.
The current Modbus protocol specification does not define register usage. However, there is an informal obsolete
register numbering convention (see
Table 5 below) which is derived from the original Modicon Modbus protocol
specification. This convention is used by many vendors of Modbus capable products.
Table 5: Register Numbering Convention
Registers Usage Valid Function Codes
00001-09999 Read/write bits (“coils”) 01 (read coils)

05 (write single coil)

15 (write multiple coils)
10001-19999 Read-only bits (“discrete inputs”) 02 (read discrete inputs)
30001-39999 Read-only 16 bit registers (“input registers”), IEEE 754
floating point register pairs, arbitrary length strings
encoded as two ASCII characters per 16-bit register 03 (read holding registers)

04 (read input registers)

40001-49999 Read/write 16-bit registers (“holding registers”, IEEE 754
floating point register pairs, arbitrary length strings
encoded as two ASCII characters per 16-bit register 03 (read holding registers)

06 (write single register)

16 (write multiple registers)
Each range of register numbers maps to a unique range of addresses that are determined by the function code and
the register number. The address is equal to the least significant four digits of the register number minus one, as
shown in
Table 6 below.
Table 6: Register Number Range Mapping
Registers Function Codes Data Type and Address Range
00001-09999 01, 05, 15 Read/write bits 0000-9998
10001-19999 02 Read-only bits 0000-9999
30001-39999 03, 04 Read-only 16-bit registers 0000-9998
40001-49999 03, 06, 16 Read/write 16-bit registers 0000-9998