Prosoft-technology 5201-MNET-ASCII Manual de usuario descargar pdf (Pagina 59)

MNET ♦ ProLinx Gateway Modbus Protocol Specification

Modbus TCP/IP Interface Module Driver Manual

ProSoft Technology, Inc. Page 59 of 78

September 1, 2010

4.4 Read Input Registers (Function Code 04)

Query

Function code 04 obtains the contents of the controller's input registers at

addresses 3xxxx. These locations receive their values from devices connected to

the I/O structure and can only be referenced, not altered from within the

controller, The addressing allows up to 125 registers to be obtained at each

request; however, the specific Server device may have restrictions that lower this

maximum quantity. The registers are numbered for zero (30001 = zero, 30002 =

one, and so on). Broadcast mode is not allowed.

The example below requests the contents of register 3009 in Server number 11.

Adr Func Data Start Reg Hi Data Start Reg Lo Data #of Regs Hi Data #of Regs Lo Error Check Field

11 04 00 08 00 01 CRC

Response

The addressed Server responds with its address and the function code followed

by the information field. The information field contains 1 byte describing the

quantity of data bytes to be returned. The contents of the registers requested

(DATA) are 2 bytes each, with the binary content right justified within each pair of

characters. The first byte includes the high order bits and the second, the low

order bits.

Because the Server interface is normally serviced at the end of the controller's

scan, the data will reflect the register content at the end of the scan. Each PC will

limit the quantity of register contents provided each scan; thus for large register

quantities, multiple PC scans will be required, and the data provided will be form

sequential scans.

In the example below the register 3009 contains the decimal value 0.

Adr Func Byte Count Data Input Reg Hi Data Input Reg Lo Error Check Field

11 04 02 00 00 E9

1 2 ... 54 55 56 57 58 59 60 61 62 63 64 ... 77 78

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Prosoft-technology 5201-MNET-ASCII Manual de usuario Pagina 59