54
votes
Accepted
Why was it common to reference memory locations using negative numbers on some BASICs?
The difference between Applesoft BASIC and the other Microsoft 6502 BASIC derivatives can be explained by the fact that Applesoft BASIC was not the first BASIC for the Apple II; the first was Apple II ...
- 1,255
39
votes
Accepted
Does AppleSoft BASIC really parse "LE THEN" as "LET HEN"?
The AppleSoft BASIC parser ignored white space for anything that was outside of double quotes ("). As well, there were only a few revisions of the Apple II ROMs that affected the BASIC parser, ...
- 19.1k
31
votes
What does this line: `T=C/2=INT(C/2)` do? Why is it valid syntax?
Explaining what this line does is easy enough: it checks if C is even by dividing it by 2 and comparing the result to its floor, then stores the result of the comparison in the variable T. Comparisons ...
- 27.3k
25
votes
Accepted
How are the randomizer values on the Apple II maintained?
It's incremented while waiting for keyboard input.
The 16-bit random seed (RNDL and RNDH) is updated by the KEYIN routine as it spins while waiting for a key press. KEYIN is used by the Monitor ROM's ...
- 1,123
23
votes
Accepted
How did the Apple IIe convert to upper case?
This is actually done as part of the Applesoft tokenizer. Basically when you type a line of code into the Applesoft interpreter, the very first thing that happens is that the line is tokenized -- it ...
- 764
20
votes
Accepted
Why does Applesoft BASIC get confused by a nonzero value at $0800?
The Applesoft RUN command ($d912) begins by calling SETPTRS ($d665), which calls STXTPT ($d697) to initialize TXTPTR ($b8-b9) to the value in TXTTAB ($67-68) minus one. In simple terms, parsing of ...
- 10k
18
votes
Accepted
What are the rules for Applesoft BASIC formatting for code?
This is an AppleSoft issue where it puts spaces either side of a token.
PET/CBM BASIC (based off the same code base) doesn't do this.
Tokenising ignores spaces, this means it can be difficult on the ...
- 5,377
18
votes
Can you read the character definitions (font) in an Apple II using PEEK in Applesoft BASIC?
No, it's not possible to read the built-in text mode font data from "inside" the machine. (Update: Except perhaps in the Apple IIgs - see below.) In all Apple II models the font data is in a ...
- 7,818
16
votes
Accepted
Looking for an accurate Apple II(e) character set - in particular, what is CHR$(133)?
The game was originally written for the TRS-80 and ported to the Apple II.
In an online TRS-80 emulator PRINT CHR$(133) is a partial vertical line.
The TRS-80 character set has other options for &...
- 7,818
14
votes
Accepted
Extensions to Apple BASIC with ampersands
After a bit of research, it turns out it was Applesoft.
The interpreter had a feature where, if it encountered an ampersand during execution of the program, it would unconditionally jump to a ...
- 5,257
14
votes
Apple IIe SYNTAX ERROR
If an Apple II boots without DOS, then the prompt you get only understands built-in Applesoft commands such as PRINT and LIST. Without DOS, the disk commands such as CATALOG will not be available (and ...
- 7,119
14
votes
Accepted
Help understanding TAIPAN source code for the Apple II
You don't need to follow the listing far to see the problem.
Line 10 ends with GOTO 10000, and 10000 starts with CALL 6147, which is $1803, smack in the middle of the Applesoft source code, which ...
- 7,818
14
votes
Merge two (saved) Apple II BASIC programs in memory
The Applesoft Toolkit provided a number of extensions to Applesoft Basic via the ampersand hook.
The renumbering function was probably the most frequently used, but it also provided "hold" ...
- 34.3k
14
votes
Can you remove a variable in the 8-bit Microsoft BASICs?
So the question is, does a variable which no longer has a value still have any footprint in RAM,
Yes, the table entry for a variable persist for the whole runtime of a program. Those tables are only ...
- 249k
13
votes
Accepted
Why does the Applesoft BASIC have shapes?
Why did Apple include shapes in Applesoft BASIC?
Because they were introduced with the 'Programmers Aid #1 ROM' for Integer BASIC, so it was rather natural for Applesoft to support it as well.
...
- 249k
13
votes
Accepted
Are there standalone emulators of Applesoft Basic?
Yes, there are at least a couple:
LinApple - for Linux/Raspberry Pi. This fork of LinApple is current and maintained, and fixes annoying configuration bugs that others hadn't addressed.
AppleWin — for ...
- 22.6k
12
votes
Accepted
Where can I find the Applesoft line-drawing algorithm?
You can find the hi-res drawing code in an Applesoft disassembly. HPLOT starts at $F6FE.
The ROM code is optimized for size, and parts are tricky to sort out. If you want something a bit more ...
- 10k
12
votes
What are the rules for Applesoft BASIC formatting for code?
Here is a program I wrote several years ago in AppleSoft for the fun of it. What it simply does is disassemble itself from the tokenized storage into a listing. If you run it, it will look the same as ...
- 19.1k
12
votes
What does this line: `T=C/2=INT(C/2)` do? Why is it valid syntax?
The line in question is T=C/2=INT(C/2)
The first '=' is a variable assignment.
The second '=' is part of the expression and is an equality test.
The expression returns a boolean result, which is ...
- 5,313
11
votes
How to use HGR2 (or HGR) on an Apple II
Problem
Here is a picture (to scale) of how memory is being used in
units of "pages" (256 bytes) on the Apple 2.
000000001111111111111111 2222222222222222 3 ... ... 9
...
- 730
11
votes
Applesoft (pseudo) Random Numbers - alternatives?
I found an example that plotted on the hi-res screen to evaluate a replacement RNG. The code is based on a Call-A.P.P.L.E. article from 1989, available here. It appears to be a linear congruential ...
- 10k
11
votes
How did the Apple IIe convert to upper case?
This post has a brief history of Applesoft. You'll note it was modified in 1984 to allow entry of lower-case keywords.
If you look at the PARSE routine (at $d56c) in the ][+ version of Applesoft in ...
- 10k
10
votes
Accepted
Turn off Apple IIe sound
In this case, to "toggle" the speaker means to move it from one position to the other. To make a sound, you repeatedly toggle the speaker (by poking that address) at a particular speed to make a sound ...
- 7,119
10
votes
How can I run a machine language program off the disk drive on an Apple II?
In Apple DOS simply
BRUN nameoffile
if it is an executable binary (type B in CATALOG) it will load and call the machine language at the address that was used to save the binary. If it is just a blob ...
- 4,798
9
votes
Extensions to Apple BASIC with ampersands
While paxdiablo answered the question confirming that it was AppleSoft, I can point out three things related to it as an extension:
When you load your extension, it should attempt to relocate itself ...
- 19.1k
9
votes
How did the Apple IIe convert to upper case?
[Oioioi, this is one of the darkest corner of the II line :))]
How did the Apple IIe convert to upper case?
The Apple IIe did not convert at all. That's why the IIe Programmers Reference mentions:
.....
- 249k
8
votes
In Applesoft BASIC, does combining statements into a single line speed up execution?
Yes. Replacing NEXT I with NEXT will also help.
One way to evaluate this is to throw a speaker click (PEEK -16336) into the loop and listen. The faster the loop, the higher the pitch. (Then try it ...
- 10k
8
votes
Merge two (saved) Apple II BASIC programs in memory
There is no built-in facility for merging BASIC programs. They're stored in tokenized form and can't simply be stuffed together. @scruss identified a simple approach in a comment: save one of the ...
- 10k
8
votes
Does AppleSoft BASIC really parse "LE THEN" as "LET HEN"?
This is not specific to AppleSoft BASIC. Whitespace was generally not significant when recognizing keywords in the original Dartmouth BASIC, either. This allows you to write something like
LETA=100
...
- 2,691
8
votes
Does AppleSoft BASIC really parse "LE THEN" as "LET HEN"?
Possible explanation
I think I have found a possible reason why the code was submitted with such a dubious variable name, without the issue being caught.
The information section under the video, What ...
- 5,001
Only top scored, non community-wiki answers of a minimum length are eligible