GE EPM 9650/9800 manual Function Code 23H Read Holding Registers Multiple Times

1.8.1: Function Code 23H - Read Holding Registers Multiple Times

This function allows a Master station to read the binary contents of holding registers (4X references) in the slave multiple times. Broadcast is not supported.

The Master device sends a packet defining the starting register, quantity of registers to be read and the repeat count. Registers are addressed starting at zero: registers 1-16 are addressed as 0-15.

Here is an example of a request to read registers 40108-40110 twice from slave device 17:

Function Code
Field Name	Example (Hex)
Slave Address	11
Function Code	23
Data Starting Address Hi	00
Data Starting Address Lo	6B
Number of Registers Hi	00
Number of Registers Lo	03
Repeat Count	02
Error Check (LRC or CRC)	--

The register data in the response message are packed as two bytes per register, with the binary contents right justified within each byte. For each register, the first byte contains the high order bits and the second contains the low order bits.

Data is scanned at the following maximum rates, depending on the repeat count:

Repeat Count	RTU Framing	ASCII Framing
1	509 Registers	253 Registers
2	254 Registers	126 Registers
3	169 Registers	84 Registers
4	127 Registers	63 Registers
5	101 Registers	50 Registers
6	84 Registers	42 Registers
7	72 Registers	36 Registers

The response is returned when the data is completely assembled.

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