GE GFK-1541B manual Command 3003, Example

4

Command 3003, Example 2

Read nine (9) Input Discretesfrom Address 10005 in the remote Modbus/TCP server. Store the registers at location %T3(bit mode). Return the COMMREQ Status word to %R10.

	Dec	(Hex)
Word 1	00008	(0008)	Length of Channel command Data Block (8–14 words)
Word 2	00000	(0000)	Always 0 (no-wait mode request)
Word 3	00008	(0008)	Memory type of CRS word (%R)
Word 4	00009	(0009)	CRS word address minus 1 (%R10) *
Word 5	00000	(0000)	Reserved
Word 6	00000	(0000)	Reserved
Word 7	03003 (0BBB)		Read from a Modbus/TCP Device
Word 8	00006	(0006)	Channel number (6)
Word 9	00002	(0002)	Modbus Function Code
Word 10	00074	(004A)	Local PLC Memory Type
Word 11	00003	(0003)	Local PLC Starting Address
Word 12	00005	(0005)	Address in the Remote Device
Word 13	00009	(0009)	Number of Input Discretes to Read from the Remote Device
Word 14	00001	(0001)	Unit Identifier

*Word 4 (CRS word address) is the only zero-based address in the Command Block. Only this value requires subtracting 1 from the intended address.

(Word 7) Channel Command Number: Word 7 identifies the COMMREQ as a Read Data from Modbus/TCP Device command block.

(Word 8) Channel Number: Word 8 identifies the channel number previously allocated for communication with the remote Modbus/TCP server.

(Word 9) Modbus Function Code: Word 9 specifies Modbus Function Code 2, Read Input Status.

(Word 10) Local PLC Memory Type: Words 10-11 specify the location in the local PLC where the Ethernet Interface will store data received from the remote device . Valid values for Word 10 are listed on page 4-14.

(Word 11) Local PLC Memory Address: Word 11 determines the starting address in the local PLC in which the data from the remote device is to be stored. The value entered is the offset (1- based) from the beginning of PLC memory for the memory type and mode specified in Word 10. This offset will be either in bits, bytes, or words depending on the mode specified. Valid ranges of values depend on the PLC’s memory ranges. The user is responsible for assuring that this area is large enough to contain the requested data without overwriting other application data.

(Word 12) Remote Device Address: Word 12 specifies the address in the remote Modbus/TCP device.

(Word 13) Number Registers in Remote Device: Words 13 specifies the quantity of input

discretes to read from the remote device.

(Word 14) Unit Identifier: Default is 1. This field is typically used by Ethernet to Serial bridges to specify the address of a Modbus Slave on a multidrop link. The Modbus/TCP Unit Identifier is a special control code used in a Modbus/TCP message block. This value is 1 for most Modbus/TCP messages.

4-14 TCP/IP Ethernet Communications for the Series 90™ PLC User's Manual– May 2002 GFK-1541B