Contatto
MCP 4 – User's manual
DUEMMEGI
Regarding the functions used by MCP4 in MODBUS MASTER mode, the following rules apply:
➢
If the specified WORD number is in the range 00000 to 30000, MCP4 performs reading via function 3
(Read Holding Registers) and writing via function 16 (Write Multiple Registers). The words read/written
are those mapped from WORD 00000 to 30000 in the slave
➢
If the specified WORD number is in the range 30001 to 39999, MCP4 performs reading via function 4
(Read Input Registers) and no writing (being “Input” registers, thus read only). The words read are those
mapped from WORD 0000 to 9998 in the slave
➢
If the specified WORD number is in the range 40001 to 49999, MCP4 performs reading via function 3
(Read Holding Registers) and writing via function 16 (Write Multiple Registers). The words read/written
are those mapped from WORD 0000 to 9998 in the slave
➢
If the specified WORD number is in the range 50001 to 65535, MCP4 performs reading via function 3
(Read Holding Registers) and writing via function 16 (Write Multiple Registers). The words read/written
are those mapped from WORD 9999 to 25534 in the slave
The following table resumes what just listed:
Word in the directive
MCP 4
Word in the slave
Used MODBUS
function
00000 ÷ 30000
00000 ÷ 30000
3 [R] and 16 [W]
30001 ÷ 39999
0000 ÷ 9998
4 [R]
40001 ÷ 49999
0000 ÷ 9998
3 [R] and 16 [W]
50000 ÷ 65535
9999 ÷ 25534
3 [R] and 16 [W]
Notes:
•
The numbers shown in the previous table are all in decimal format.
•
The first case (Word 00000 ÷ 30000) may seem redundant because it is already included in the last two, and in fact it is, but
allows the back compatibility with FW versions of MCP 4 less than 1.7.
Page 10 of 87
Rel.: 1.2 October 2018
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