5

4575D–BCD–09/05

ATA6830

3.2

Digital Part

Figure 3-2.

Digital Blocks

Figure 3-2 shows all digital blocks of the circuit. The stepping motor will be controlled by com-

mands via the bus input pin. An analog comparator is used as a level shifter at the input. There

is also a possibility of clamping the bus pin to ground. This will be used after detecting an error to

feedback this to the microcontroller.

The next block is a UART. Its task is clock recovery and data recognition of the incoming bit

stream. For clock recovery a special bitstream is used after each power on. The generated bit-

stream will be analyzed and after a correct parity check interpreted for execution.

A sophisticated cruise control generates all control signals for the two H-bridge drivers. It uses

an internal step-time table for accelerating and decelerating the stepping motor depending on

the actual and desired position and the temperature and voltage levels. Exception handling is

integrated to interpret and react on the temperature, supply voltage, and coil-current signals

from the analog part.

UART

Clock

Recovery

Bitstream

Recovery

Data

Recognition

&

Parity-Check

bitstream

rxd

shiftclk

BUS

VREF

reference run

new position

Step Time Memory

Maximum Step Time

New Step Time

Clk

Voltage Levels

Actual Step Time

Cruise Control

Desired Position

Instantaneous Position

Stepper Motor Control

Error Timer

Error Signals

Temperature Signals

Error Signals

Reset