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Newbie Assembly

I'm just starting to learn Apple II assembly using the mini-assembler on my
platinum //e. I'm using the instruction listing, Appendix A of the "Apple II
Reference Manual".

I've written this program which clears the HGR screen to a colour (white by
default). It works! Can someone help me to see if this is an optimal way of
doing this?

300:    LDA #FF
302:    LDX #3F
304:    LDY #00
306:    STX $030E
309:    STY $030D
30C:    STA $0100
30F:    DEY
310:    BNE $0306
312:    DEX
313:    CPX #19
315:    BNE $0304

You can change to a different colour by putting the bit-pattern into $0301.

thanks,
Simon.