date

page

04/2010

5 of 8

APPLICATION NOTES

Encoder operational mode

• Initiation mode: At power up the encoder starts by doing:

– Coarse channel measurement

– Fine channel measurement

– Combine fine with coarse for ABS position (natural binary)

The above takes about 1 ms. After this, the encoder switches to continuous operation.

• Tracking mode: Only the Fine channel is active and the MCU internal position register is updated with

data from Fine:

– MCU 12 bit position register is updated from Fine every 125 μs.

– The MCU position register can be lagging up to 120 μs from the real position. This error is

proportional to speed: e<0.75 deg/1k(rpm).

– The MCU is able to follow up to speeds of 8000 RPM and recover to full accuracy when speed

slows down.

– For accurate position update without above time delay, outputs for incremental A quad B or Count

and Up/Dwn from the Fine channel are provided. These outputs are operational up to 8000 RPM

and there is no speed error. There is an acceleration error dependent on an internal filter constant

of about 100 μs.

– When using the incremental output there also is an Index output available, with one index pulse

per 1/16 turn.

• Initiation mode can be repeated at standstill on command from the master MCU in the application.

– Loop time ~1 ms.

Serial Peripheral Interface Commands

The SPI or Serial Peripheral Interface Bus is a standard interface promoted by Motorola and Microchip among

others. It consists of 4 signals:

MOSI: Master Out Slave In

MISO: Master In Slave Out

SCK: Serial Clock

CSB: Chip Select Bar (active low)

SPI BUS

The SPI bus runs full duplex and transfers multiples of 8 bits in a frame. The SPI type is the most common

(CPOL=0, CPHA=0), also known as Microwire. Data is captured on the rising edge of SCK and the output data is

changed after the falling edge of SCK.

SCK

MISO

MOSI

CSB

MSB

LSB

MSB

LSB

Serial Peripheral Interface Bus (SPI) on AMT1025

Setup

phone 503.612.2300

fax 503.612.2380 www.cui.com

PART NUMBER:

DESCRIPTION:

AMT203

12 BIT ABSOLUTE ENCODER