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@ -123,7 +123,7 @@ You've just drawn the word "HELLO" the fastest possible way with Applesoft only.
The problem now is that to `PRINT`/draw all possible combinations of colors you need to be able to `PRINT` all 255 possible values of bytes, including those between 128 to 159, that is the control-characters.
As print is super-fast compared to `PLOT` (or `HLIN` and `VLIN`), this could be used to display sprites on the lores screen.
As `PRINT` is super-fast compared to `PLOT` (or `HLIN` and `VLIN`), this could be used to display sprites on the lores screen faster than ever with Applesoft.
And since what we want to do is use combinations of CTRL-characters to change the text mode **within** strings, we could draw any shape and store the `INVERSE`/`FLASH`/`NORMAL`/`SPECIAL` statements within the string itself !
@ -132,7 +132,7 @@ The routine will be simple and short, so we can store it in $300. But if you wan
The first thing we want to do is initialize CSWL/CSWH (and thus activate our routine). To do that we can begin in $300 with a simple init routine that needs to be called at the start of your Applesoft program (or at least before you want to take advantage of the new feature).
We also want to initialize a flag stating that the "Peculiar mode" is not set yet. The Peculiar mode is that new mode where we allow to print control-characters. I decided that this flag would be stored in zero page $34. This memory location is normally used by the monitor (it is known as `YSAV`) to store temp data but I estimated that there would be no interest in being in the monitor AND want to print control-characters on the lores screen. As this is the only zero page location that I need, I wanted to avoid any of the usual "free" zero pages locations to make sure I don't interfere with possibly other programs that might use these "free" locations.
We also want to initialize a flag stating that the "Peculiar mode" is not set yet. The "Peculiar mode" is that new mode where we allow to print control-characters. I decided that this flag would be stored in zero page $34. This memory location is normally used by the monitor (it is known as `YSAV`) to store temp data but I estimated that there would be no interest in being in the monitor AND want to print control-characters on the lores screen. As this is the only zero page location that I need, I wanted to avoid any of the usual "free" zero pages locations to make sure I don't interfere with possibly other programs that might use these "free" locations.
So the code begins with:
@ -155,8 +155,8 @@ So the first thing we will do is save the values of `A` and `X`. Why these two ?
We will save `A` on the stack and `X` in a zero page location named `YSAV1` (in `$35`). This location is used by `COUT1` to save the value in `Y` and restore it when leaving. It's not used elsewhere meaning we can use it for the same purpose (except we're going to save `X`) until we actually call `COUT1`.
Then we are going to verify the value in `A`:
- if it's CTRL-P then we set the "Peculiar mode" flag on (by writing $FF in it), restore A and X and call `COUT1`
- if it's CTRL-F then we call the `FLASH` routine in `$F280`, this modifies `A` and `X` registers (X being now $40, the value of the FLASH-mask), we clear `X` and use `X` to reset the "Peculiar mode" flag, we restore `A` and `X` and call `COUT1`
- if it's CTRL-P then we set the "Peculiar mode" flag on (by writing $FF in it, the important thing being that the hi-bit is set), restore `A` and `X` and call `COUT1`
- if it's CTRL-F then we call the `FLASH` routine in `$F280`, this modifies `A` and `X` registers (`X` being now $40, the value of the FLASH-mask), we clear `X` and use `X` to reset the "Peculiar mode" flag, we restore `A` and `X` and call `COUT1`
- if it's CTRL-O then we call the `INVERSE` routine in `$F277`, this again modifies `A` and `X` but `X` is now zero. We use `X` to reset the "Peculiar mode" flag, we restore `A` and `X` and call `COUT1`
- if it's CTRL-N then we call the `NORMAL` routine in `$F273`. Just like the `INVERSE` routine, this modifies `A` and `X` and `X` is now zero. Again, we use `X` to reset the "Peculiar mode" flag, we restore `A` and `X` and call `COUT1`
- if it's any other character, then we check the "Peculiar mode" flag. If it's off, we call `COUT1`. If it's on then we need to modify the value of `A` so it fits within $80-$9F. More about that in a moment.
@ -192,10 +192,9 @@ Here's the code so far:
337: 4C F0 FD JMP COUT1 ; DISPLAY THE CHARACTER IF POSSIBLE
33B: A6 34 CHK_P_MODE LDX PECULIAR_MODE ; LOAD PECULIAR MODE FLAG IN X
33D: E0 FF CPX #$FF ; IS THE FLAG SET ?
33F: D0 F4 BNE OUT0 ; IF NOT, OUTPUT THE CHARACTER
33D: 10 F6 BPL OUT0 ; IF HIBIT NOT SET, THEN NOT IN P-MODE, OUTPUT THE CHARACTER
341: P_MODE
33F: P_MODE
```
Now the only thing left to do is handle the "Peculiar mode". Because this mode is meant to be used with `PRINT` and `PRINT` only (while showing the lores screen), we need to check first if we're busy `PRINT`ing text or if we're doing something else like `LIST` for instance. If the command was `LIST`, we don't want to display weird characters. For example all the space characters (value 32) would be replaced with @ (value zero).
@ -204,7 +203,7 @@ The way I've found to detect if we're `PRINT`ing something is to check the stack
So, if our routine was indirectly called from Applesoft, the stack (from the last stacked value) looks like this: `66 DB 4B DB`.
`$DB66`(+1) is the return address to `OUTDO`, while `$DB4B`(+1) is the return address from the `PRINT` command. The interesting byte in the stack is the 4th. This byte will **never** be `$DB` if our routine comes from anything else but `PRINT`. So, we just need to check the value of the 4th byte. Well, in fact the **5th** byte, because our own routine adds the value of `A` to the stack.
`$DB66`(+1) is the return address to `OUTDO`, while `$DB4B`(+1) is the return address from the `PRINT` command. The interesting byte in the stack is the 3rd. We can assume this byte will **never** be `$4B` if our routine comes from anything else but `PRINT`. So, we just need to check the value of the 3rd byte. Well, in fact the **4th** byte, because our own routine adds the value of `A` to the stack.
So if we were not `PRINT`ing, we simply ignore the Peculiar mode and call `COUT1`. But if we're `PRINT`ing we do a bit more work.
@ -214,26 +213,26 @@ The small setback is that this routine uses `Y`. So far we have not used `Y`. We
Here goes:
```Assembly
341: BA P_MODE TSX ; GET STACK POINTER TO X
342: BD 05 01 LDA STACK+5,X ; GET MSB OF THE RETURN ADDRESS
345: C9 DB CMP #$DB ; IS IT FROM PRINT IN $DB49 ?
347: D0 EC BNE OUT0 ; NO, LET'S CALL COUT1 THEN
33F: BA P_MODE TSX ; GET STACK POINTER TO X
340: BD 05 01 LDA STACK+5,X ; GET MSB OF THE RETURN ADDRESS
343: C9 DB CMP #$DB ; IS IT FROM PRINT IN $DB49 ?
345: D0 EC BNE OUT0 ; NO, LET'S CALL COUT1 THEN
349: 68 PLA ; GET CHARACTER VALUE BACK FROM STACK
34A: C9 A0 CMP #$A0 ; IS IT A CONTROL CHAR (<160)
34C: 90 E8 BCC OUT1 ; YES, LET'S CALL COUT1 THEN
347: 68 PLA ; GET CHARACTER VALUE BACK FROM STACK
348: C9 A0 CMP #$A0 ; IS IT A CONTROL CHAR (<160)
34A: 90 E8 BCC OUT1 ; YES, LET'S CALL COUT1 THEN
34E: AA TAX ; SAVE CHAR IN X
34F: 98 TYA ; SAVE Y IN A
350: 48 PHA ; STORE VALUE OF Y ON STACK
351: 8A TXA ; GET BACK CHAR FROM X
352: 29 9F AND #$9F ; CLEAR BITS 5 & 6, RANGE IS NOW $80-$9F
354: 20 F0 FB JSR STORADV ; FORCE DISPLAY OF CHAR
357: 68 PLA ; RESTORE VALUE OF Y FROM STACK
358: A8 TAY ; BACK TO Y
359: 8A TXA ; RESTORE A FROM X
35A: A6 35 LDX YSAV1 ; RESTORE X FROM YSAV1
35C: 60 RTS ; RETURN TO CALLER
34C: AA TAX ; SAVE CHAR IN X
34D: 98 TYA ; SAVE Y IN A
34E: 48 PHA ; STORE VALUE OF Y ON STACK
34F: 8A TXA ; GET BACK CHAR FROM X
350: 29 9F AND #$9F ; CLEAR BITS 5 & 6, RANGE IS NOW $80-$9F
352: 20 F0 FB JSR STORADV ; FORCE DISPLAY OF CHAR
355: 68 PLA ; RESTORE VALUE OF Y FROM STACK
356: A8 TAY ; BACK TO Y
357: 8A TXA ; RESTORE A FROM X
358: A6 35 LDX YSAV1 ; RESTORE X FROM YSAV1
35A: 60 RTS ; RETURN TO CALLER
```
And here's the full code:
@ -245,11 +244,11 @@ And here's the full code:
320: 00 F0 10 C9 8F D0 05 20
328: 77 F2 F0 07 C9 8E D0 0B
330: 20 73 F2 86 34 68 A6 35
338: 4C F0 FD A6 34 E0 FF D0
340: F4 BA BD 05 01 C9 DB D0
348: EC 68 C9 A0 90 E8 AA 98
350: 48 8A 29 9F 20 F0 FB 68
358: A8 8A A6 35 60
338: 4C F0 FD A6 34 10 F6 BA
340: BD 04 01 C9 4B D0 EE 68
348: C9 A0 90 EA AA 98 48 8A
350: 29 9F 20 F0 FB 68 A8 8A
358: A6 35 60
```
## Disabling the OS
In order to activate the feature, a simple `CALL 768` is enough. But before anything, you must disable DOS (or PRODOS).