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7800 SERIES S7800A1142 KEYBOARD DISPLAY MODULE

65-0288-1 38

APPENDIX E: MODBUS FUNCTION

See Appendix A pages 26 and 27 for Setup.

OPERATION

The S7800 ModBus

Data Feature enables terminal 1, 2 to

Data + and Data -. Table 17 provides register mapping. It

identifies the mapping of the 7800 SERIES parameters to

ModBus

registers.

Function Codes

Supported function codes of Modbus Protocol Reference

Guide (PI-MBUS-300 Rev. J) are 3, 4, 6, and 17. Function

codes 3 and 4 are treated the same by the S7800. Two

registers need to be read when the data format is a U32 value

(4 bytes); if both registers are not read, then a data value of 0

(zero) is returned. U32 values are in little endian format. The

maximum number of addresses that can be queried is 127

(0x7F) for each query message.

Tables 3 through 7 provide information on the function codes.

NOTE: All Query and Response cells below are 1 byte.

Table 10. Query Message Format for Function Codes 3 and 4.

Table 11. Response Message Format for Function Codes 3 and 4.

Table 12. Query Message Format for Function Code 6 (Broadcast is supported by using a slave address of 00).

Table 13. Response Message Format for Function Code 6 (There is no response if the query was broadcast.)

Table 14. Query Message Format for Function Code 17.

NOTE: See Table 18 for function code 17 response format.

Table 15. Exception Response Message Format.

Table 16. Exception Codes.

Rr 2 Õõ

Ss 3Öö

Tt 4Úú

Uu 5 Ùù

Vv 6Ûû

Ww 7 Ü ü

Xx 8Çç

Yy 9Ññ

Zz Ÿÿ

Table 9. Edit Available Text and Characters. (Continued)

Edit Available Text

and Characters

Slave Address

Function

Code

Starting

Address High

Starting

Address Low

Number of

Addresses High

Number of

Addresses Low CRC CRC

01 03 00 0A 00 01 A4 08

Slave Address Function Code Byte Count Data High Data Low CRC CRC

01 03 02 00 22 38 5D

Slave

Address

Function

Code

Starting

Address High

Starting

Address Low

Preset Data

High

Preset Data

Low CRC CRC

01 06 00 7F 00 04 B9 D1

Slave

Address

Function

Code

Starting

Address High

Starting

Address Low

Preset Data

High

Preset Data

Low CRC CRC

01 06 00 7F 00 04 B9 D1

Slave

Address

Function

Code CRC CRC

03 11 C1 4C

Slave

Address

Function

Code

+ 80h

Exception

Code

CRC CRC

Exception

Code Definition Description

01 Illegal

Function

An illegal function as requested. Only

3, 4, 6 and 17 are supported.

02 Illegal

Data

Address

Too many bytes requested, address

is out of range, register is read only,

or the number of address requested

is past the last register.

03 Illegal

Data

Value

The “Preset Data” from function code

6 is invalid/out of range.