I have it running with software serial port, but facing some issues.

Based on code above:

Code:
serout portc.5,t9600, [$7e,$ff,$06,$06,$00,$00,$07,$fe,$ee,$ef]   
pause 500
serout portc.5,t9600, [$7e,$ff,$06,$03,$00,$00,$02,$fe,$f6,$ef]
This works, however, it requires at least 500ms pause between each statements, or they're ignored.
Is this normal?
also, I have read the datasheet, but can't understand, which bit, based on which logic I should change in code above, to select another track, or change volume?

for example, in this code, posted above, which selects #3, #2, #1 songs in a folder, I can clearly see

Code:
hserout [$7e,$ff,$06,$03,$00,$00,$03,$fe,$f5,$ef] 
hserout [$7e,$ff,$06,$03,$00,$00,$02,$fe,$f6,$ef] 
hserout [$7e,$ff,$06,$03,$00,$00,$01,$fe,$f7,$ef]

But why there are $F5, $F6, $F7 bytes also changing at the end of the code?