You know how `SPC()` can be used to PRINT a number of space characters. For example `PRINT SPC(10)` will print 10 space characters.
Why didn't they allow to print something else than space characters ? It would have been interesting (?) to have the ability to repeat a sequence of any character.
Maybe like `PRINT REPT("*",10)` would print 10 asterisks.
But Applesoft does not provide such an instruction. So are we doomed to use `PRINT "**********"`?
Here's a technique that will allow you to repeat any character, even in `FLASH` and `INVERSE` without using additional 6502 routines.
What are those inverted single quote characters doing here ? "Something" has replaced space characters with those inverted single quotes ...
<imgsrc="spc2.png"align="left"width=200px>If you have a loaded Applesoft program, I encourage you to `LIST` it. If not, quickly type a short one and see the results ...
As you can see, something is messed up !
## Explanation
To understand what's happening here, you need to know how characters are printed on screen by Applesoft.
The general routine to print characters on screen is in `$DB5C`.
Here's the routine, taken from [S-C documentor website](http://www.txbobsc.com/scsc/scdocumentor/)
1950 * PRINT CHAR FROM (A)
1960 *
1970 * NOTE: POKE 243,32 ($20 IN $F3) WILL CONVERT
1980 * OUTPUT TO LOWER CASE. THIS CAN BE CANCELLED
1990 * BY NORMAL, INVERSE, OR FLASH OR POKE 243,0.
2000 *--------------------------------
DB5C- 09 80 2010 OUTDO ORA #$80 PRINT (A)
DB5E- C9 A0 2020 CMP #$A0 CONTROL CHR?
DB60- 90 02 2030 BCC .1 SKIP IF SO
DB62- 05 F3 2040 ORA FLASH.BIT =$40 FOR FLASH, ELSE $00
DB64- 20 ED FD 2050 .1 JSR MON.COUT "AND"S WITH $3F (INVERSE), $7F (FLASH)
DB67- 29 7F 2060 AND #$7F
DB69- 48 2070 PHA
DB6A- A5 F1 2080 LDA SPEEDZ COMPLEMENT OF SPEED #
DB6C- 20 A8 FC 2090 JSR MON.WAIT SO SPEED=255 BECOMES (A)=1
DB6F- 68 2100 PLA
DB70- 60 2110 RTS
The routine is called with the accumulator containing the character to print every time Applesoft needs to print something (like when using `PRINT` or `INPUT` or ... `SPC` !)
The routine that will effectively print the character on screen is `COUT` (in `$FDED`here named `MON.COUT`) but this routine here is the pre-treatment of the character to print.
As you can see, before calling `MON.COUT`, an `ORA` with zero-page memory `$F3` is executed. This `ORA` is needed to display characters in flash mode. The problem is that `$F3`, even after a `CTRL-BREAK` is not reset and still contains `#$40` (decimal 64), meaning that Applesoft is still (partially -- see below why) in flash mode.
But if it's in flash mode, how comes it prints NORMAL single quotes and not flashing characters ? Because `$F3` is just a mask and is not enough to flash the characters on screen. Another mask, in zero-page `$32` is also used, but this time by the `MON.COUT` routine. In fact `$32`is usually considered to be the memory that indicates if we are in normal (value `#$FF`, decimal `255`), flash (value `#$7F`, decimal `127`) or inverse (value `#$3F`, decimal `63`) modes. But for the flash mode, the mask in `$F3` is equally primordial. In fact, even in normal and inverse modes, the value in `$F3 `has an impact since the `ORA` is called whatever the display mode is.
So, before any character is displayed on screen by Applesoft, two masking operation occur on the ASCII value of the character.
1. an `ORA` with the value in `$F3`
2. an `AND` with the value in `$32`
`CTRL-BREAK` reset the value in `$32` to `255` ("normal" display mode) but it does not touch the value in `$F3`. That's why we have these display glitches if we `CTRL-BREAK` after `FLASH`. Clearly, it's a bug.
Of course Applesoft expects and uses some specific values in `$F3` and `$32`.
