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│ SERIES: AMT21 │ DESCRIPTION: MODULAR ABSOLUTE ENCODER

date 09/10/2021

│ page 3 of 10

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RS485 INTERFACE (CONTINUED)

Extended Commands

There are some commands that require two bytes to be received before the encoder will enact them. This includes resets

and zero saves. This prevents collisions and allows the encoder to be fully functional while sharing the bus with other

encoders.

Note that there are no responses to these instructions, and once received the encoder initiates an immediate reset. The

user’s system should expect to wait until the encoder is powered back up to send any follow up commands. Power on time

is listed in the electrical section above.

To send an extended command the user will send the <node address + 0x02> value (0x56 by default) followed by the

<extended command>.

Extended Commands

Function

0x5E

Set zero position (Single turn encoders only)

0x75

Reset encoder

Addressing

The AMT21 encoder supports multiple encoders on the RS485 bus. This is accomplished by giving each encoder a unique

node address. This node address is 8 bits long but the low two bits must be 0. Therefore, the encoder can have any single

byte value that is divisible by 4 which allows up to 64 encoders to share the bus.

By default, the node address is 0x54. Node addresses configurable via AMT ViewpointTM or set at factory for specific

configuration upon request.

The node address serves also as the read position command which is why it will be referred to it as the base command.

When the encoder sees a command on the RS485 it reads the first 6 bits to determine if it should be listening. If it sees its

address, then it interprets the low two bits for the command.

Low two bits

Hex

Command

0x00

Read position

0x01

Read turns counter (multi-turn encoders only)

0x02

Indicates extended command

0x03

Reserved

For simplicity the user can abstract away the various bits and simply implement multiple commands in their system. For

example:

Byte

Command

0x54

Read position

0x55

Read turns counter (multi-turn encoders only)

0x56

Begin extended command

Available RS485 Node Addresses (HEX)

54*

*Default address

Additional Resources: Product Page | 3D Model

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