This function will be used largely to report controller status information, and so a bit set to 1 indicates that the corresponding feature is currently enabled/active, and a bit reset to 0 indicates the opposite.
If an exact multiple of eight bits is not requested, the data is padded with trailing zeros to preserve the
B. Read Holding Registers (Read n Words) 03/04
The message sent to the controller to obtain the value of one or more registers is an
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Addr. | Func. | 1st Word | No. of words | CRC16 | |||
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| 3/4 | HI | LO | HI | LO | HI | LO |
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The reply sent by the controller echoes the first 2 characters received and then contains a
Addr. | Func. | Count | 1st value | 2nd value | ||
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| 3/4 |
| HI | LO | HI | LO |
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| Last value | CRC16 | ||
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| HI | LO | HI | LO |
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C. Force Single Coil (Write 1 Bit) |
| 05 | B |
The message received by the controller is 8 bytes long, consisting of the standard preamble and the address of the bit to force, followed by a
Addr. | Func. | Addr. of Bit | State |
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| 5 | HI | LO | FF/00 |
| 0 | HI | LO |
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Generally, this function will be used to control such features as Auto/Manual and Tuning.
The normal reply sent by the controller will be a
Volume II |