cui.com

date 02/12/2013

│ page 5 of 7

CUI Inc

│ SERIES: AMT203 │ DESCRIPTION: MODULAR ENCODER

APPLICATION NOTES

Encoder operational mode

• Initialization mode: At power up the encoder goes through an initiation and stabilization procedure.

This includes microprocessor stabilization and the program for combining Coarse

and Fine channel of the encoder for getting the absolute start position. This

takes

less than 0.1 seconds.

• 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 48 μs.

– 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 turn.

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 (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.

Serial Peripheral Interface Bus (SPI) on AMT203

Figure 7: SPI BUS Timing Diagram

The msb data out on MISO is valid soon after CSB goes low. The MOSI data is valid soon after the falling edge

of SCK. The Encoder drives data out on MISO as long as CSB is low.

Normally, CSB goes low, then after 8 clocks the command is interpreted. CSB high resets the

clock counter, and terminates any command sequence.

SCK

MISO

MOSI

CSB

MSB

LSB

MSB

LSB

Setup

Terminology

MSB = most significant byte

LSB = least significant byte

msb = most significant bit

lsb = least significant bit