86 lines
4.3 KiB
Markdown
86 lines
4.3 KiB
Markdown
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# Protocol
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The protocol checksum is litle-endian CRC16-MODBUS, but the data itself seems to be big-endian (network order).
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It is structured around 16bit words (read 4 returns 8 bytes).
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I have seen the "Transfer ID?" field containing 0xFF and 0x01, I am not yet sure of the putpose of this field. Most transactions it is set to 0xFF.
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## Reading
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### Read request
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```text
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┌──────────────┐
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╔═╡ Transfer ID? │
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║ └──────────────┘
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║ ┌────────────────────┐
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║ ╔═╡ Operation (3=read) │
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║ ║ └────────────────────┘
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║ ║ ┌───────────────┐
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║ ║ ╔═╡ Start address │
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║ ║ ║ └───────────────┘
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║ ║ ║ ┌────────────────────────────────┐
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║ ║ ║ ╔═╡ Number of 2-byte words to read │
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║ ║ ║ ║ └────────────────────────────────┘
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║ ║ ║ ║ ┌─────────────────┐
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║ ║ ║ ║ ╔═╡ Transaction CRC │
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║ ║ ║ ║ ║ └─────────────────┘
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┌╨─┬╨─┬──╨──┬──╨──┬──╨──┐
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│FF│03│00 0C│00 08│91 d1│
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└──┴──┴─────┴─────┴─────┘
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```
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### Read response
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```text
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┌──────────────┐
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╔═╡ Transfer ID? │
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║ └──────────────┘
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║ ┌────────────────────┐
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║ ╔═╡ Operation (3=read) │
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║ ║ └────────────────────┘
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║ ║ ┌──────────────────────────┐
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║ ║ ╔═╡ Number of bytes returned │
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║ ║ ║ └──────────────────────────┘
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║ ║ ║ ┌──────┐ ┌─────────────────┐
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║ ║ ║ ╔═╡ Data │ │ Transaction CRC ╞═╗
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║ ║ ║ ║ └──────┘ └─────────────────┘ ║
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┌╨─┬╨─┬╨─┬╨──────────────────────────────────────────────┬──╨──┐
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│FF│03│10│20 20 20 20 4D 4C 32 34 32 30 20 20 20 20 20 20│FD 17│
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└──┴──┴──┴───────────────────────────────────────────────┴─────┘
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```
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This particular memory section contains the device SKU: ML2420
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## Writing
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### Write request
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```text
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┌──────────────┐
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╔═╡ Transfer ID? │
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║ └──────────────┘
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║ ┌────────────────────┐
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║ ╔═╡ Operation (6=read) │
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║ ║ └────────────────────┘
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║ ║ ┌─────────┐
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║ ║ ╔═╡ Address │
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║ ║ ║ └─────────┘
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║ ║ ║ ┌──────┐
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║ ║ ║ ╔═╡ Data │
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║ ║ ║ ║ └──────┘
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║ ║ ║ ║ ┌─────────────────┐
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║ ║ ║ ║ ╔═╡ Transaction CRC │
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║ ║ ║ ║ ║ └─────────────────┘
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┌╨─┬╨─┬──╨──┬──╨──┬──╨──┐
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│FF│06│01 0A│00 01│7C 2A│
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└──┴──┴─────┴─────┴─────┘
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```
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The data at 0x010A is a boolean controlling the load output switch.
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### Write response
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Seems to return exactly the same as the data written,
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presumably to allow verifying that the data did indeed get written.
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