Hi Ping,

Driving a stepper motor using assembly code and an 8051 by RS232 is not difficult actually.

1. U need to first define where u intend to use this motor. There are many kinds of stepper motors available. The sizes depend on the Torque, Phase, and Power requirement.

2. Once u have define item 1, then u may look at the two kinds of topologies used to drive stepper motors. There are two kinds available, namely Bipolar & Unipolar.

3. Why this is important is because, the chips that will be connected to the 8051 would depend on the motor & topologies being applied.

This location explains this better:

1.http://zone.ni.com/devzone/d...endocument

or u may look for this book "The Microcontroller Idea Book" that shows examples in chapter 11.

Ranjit