Jake In The Caves - Illegal Function Call in 4640

Master (175)

15-09-2022, 01:19

OK Guys, looking for a little advice on tracing this Error ! The line in question is :-

4640 POKE I,VAL("&H"+A$)

So my understanding is that POKE is writing data to a specific memory address. I don't fully understand memory addresses,bus addresses, stacks, registers etc so errr yea but I'm currently assuming its got something to do with the all those DATA statements. However a little help in narrowing the search would be appreciated as I've little experience in tracing issues with a command of this type. Syntax is easy, others not so much but i can follow the program structure in some cases but this command is foreign to me :/

The program listing can be found in Nr 13 MSX Computer Magazine Page 57.

https://www.msxcomputermagazine.nl/archief/mcm-13/

Dank u well

Paul

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By gdx

Enlighted (6438)

15-09-2022, 02:28

Illegal function call occurs when the parameter after the comma is incorrect. A$ has probably taken a bad value. What is A$ worth when the error occurs? It should be a string of one or two characters corresponding to a hexadecimal value between 0 and FF.

By Manuel

Ascended (19683)

15-09-2022, 07:38

This part of the program is poking bytes into memory, probably a machine code program. You made a mistake in the data lines. You can use the ICP program to check whether the typed in lines are correct... That's the best way.

By ro

Scribe (5061)

15-09-2022, 08:25

aaaaaah, the old Jake In The Caves. I used too like this one very much. Wasn't it Stefan van der Loef who wrote that?

By Hit-Biter

Master (175)

15-09-2022, 09:38

Thanks guys, I suspected it was a DATA issue. Manuel or someone can you eleborate on the ICP Program ? I assume its some sort of checksum program as i see the checksum values on the side of the listing.

By Hit-Biter

Master (175)

15-09-2022, 09:51

gdx wrote:

How do i check the value of A$ ? PRINT A$ after the program crashes ?

By gdx

Enlighted (6438)

15-09-2022, 10:05

Yes, just after the error occurs.

By Hydragon

Paladin (751)