CUI DEVICES | SERIES: AMT21 | DESCRIPTION: MODULAR ABSOLUTE ENCODER

date 08/05/2022 | 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

00

0x00

Read position

01

0x01

Read turns counter (multi-turn encoders only)

10

0x02

Indicates extended command

11

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)

00

20

40

60

80

A0

C0

E0

04

24

44

64

84

A4

C4

E4

08

28

48

68

88

A8

C8

E8

0C

2C

4C

6C

8C

AC

CC

EC

10

30

50

70

90

B0

D0

F0

14

34

54*

74

94

B4

D4

F4

18

38

58

78

98

B8

D8

F8

1C

3C

5C

7C

9C

BC

DC

FC

*Default address

Additional Resources: Product Page | 3D Model