AN2350 datasheet(21/41 Pages) STMICROELECTRONICS

21 / 41 page

AN2350

Hardware and mechanical equipments

21/41

Figure 14.

The encoder ring of one DC motor

The sectors D, A and B represent the absolute encoder, while the sector C represents the

incremental encoder.

The opaque parts of each sector of the absolute encoder are placed according to a Gray

code, in order to offer absolute position of the link with a resolution of 45 degrees. In this way

it is possible to identify 8 angular positions accordingly to the scheme below, where the

sector D (white wire) represents the most significant bit of the encoder, while the sector A

(grey wire) represents the least significant bit.

Table 4.

The sectors of the absolute encoder

In order to capture every transition, in each bit of the absolute encoder has been developed

a logic circuit with NAND ports. A detail of the conditioning circuit for one of the absolute

encoders of the wafer handler is shown in Figure 15. In this way the output of this circuit can

be associated to an external interrupt of the microcontroller, while the output bits of the

absolute encoder can be associated to three GPIOs (General Purpose Input Output) in

order to read its value.

Angular position

Sector D

(white wire)

Sector B

(Violet wire)

Sector A

(Grey wire)

Absolute

encoder values

b2b1b0

AN2350 Datasheet(PDF) 21 Page - STMicroelectronics