AN1495

Code

Doc ID 8700 Rev 3

21/25

Appendix B

Code

The following is an except from the firmware which executes on the ST7264 based control

which is part of the PractiSPIN™ evaluation system. This code segment is executed when

the decision has been made that it is time for the L6208 to take the next microstep (either

forward or reverse).

; PB.4 is the L6208 clock pin

; PB.5 is the L6208 reset pin

; stepstate is a byte variable which controls the motor stepping.

; torquscaler is a byte used to modulate the normalized sine wave values

read from the table to set the current level

; TAOC1LR is a register that controls Vrefa (via the duty cycle into the low

pass filter)

; TBOC1LR is a register that controls Vrefb (via the duty cycle into the low

pass filter)

bres PBDR,#4

;take clock back low ready to generate rising edge later

bset PBDR,#5

;normal state for reset jumpifflagclear forward,

doclockrev; jump if direction is reverse

;direction is forward

inc stepstate

jrne for002

; skip if stepstate has not rolled over to zero

bres PBDR,#5

; activate reset to maintain sync (just for added noise

immunity insurance)

for002:

ld a,stepstate

and a, #%00011111 ; use only lower five bits as index for table lookup

ld x,a

; save index

; on indexes 8 and 9, clock L6208 to sequence through zero and then polarity

reversal and a, #%00001110

cp a, #8

; 8 or 9

jrne for001

bset PBDR,#4

; rising edge for clock

for001:

ld a, (microtable1,x); get normalized value from table

ld y, torquescaler

mul y,a

; y:a = (table value) * torquescaler

ld TAOC1LR,y

; duty cycle = (table value) * torquescaler/256

; repeat for phase B