Stepper motors are very accurate motors that are commonly used in computer disk drives, printers and clocks. Unlike dc motors, which spin round freely when power is applied, stepper motors require that their power supply be continuously pulsed in specific patterns. For each pulse, the stepper motor moves around one ‘step’, often 7.5 degrees (giving 48 steps in a full revolution).
There are two main types of stepper motors - Unipolar and Bipolar. Unipolar motors usually have four coils which are switched on and off in a particular sequence. Bipolar motors have two coils in which the current flow is reversed in a similar sequence.
let dirsB = %00001111 ; make pins output
main: for b3 = 0 to 99 ; start a for...next loop
gosub lstep ; call left step sub-procedure
next b3 ; next loop
for b3 = 0 to 99 ; start a for...next loop
gosub rstep ; call right step sub-procedure
next b3 ; next loop
goto main ; repeat
lstep: let b1 = b1 + 1 ; add 1 to variable b1
gosub stepit ; do the step
return
rstep: let b1 = b1 - 1 ; subtract 1 from variable b1
gosub stepit ; do the step
return
stepit: let b1 = b1 & %00000011 ; mask lower two bits of b1
lookup b1,(%1010,%1001,%0101,%0110),b2 ; lookup code into b2
let pinsB = b2 ; output b2 onto control lines
return
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