View source for 83:OS:ROMPage0C

[[Category:83:OS Information|ROM Page 0C]]
This ROM page is loaded as soon as an ASM program is launched.

==Structure==

===Direct Calls, 4000 to 4F0B===
Here is the ROM Call jumptable, which looks like this :

 <nowiki>
 call 0033
 ret
 call 010F
 ret
 call 011B
 ret
 call 111F
 ret
 ...</nowiki>

... seldom having some jumps instead of calls.

===Indirect ROM Calls, 4F0C to 51F2===

At 4F0C, the ROM Calls start to look like this :

<nowiki>
	push	af
	ld	a,XX    
	ld	(80C8),a
	pop	af
	jr	5188
</nowiki>

Calling a routine that uses the above format in the jump table loads a table index in ASM_IND_CALL (80C8), then goes to one of two handlers. The jr address calls either PARSER_EXEC (for addresses between 4F0C and 50A9) or GRAPH_EXEC (between 510A and 51E6). PARSER_EXEC goes to page $09 and GRAPH_EXEC goes to page $04. After calling a routine in one of those two ranges, the OS calls a handler on the corresponding page that adds 2*(80C8) (memory addresses are two bytes) to the start address of the address table, puts that value on the stack, and rets to that address. 

There is a region between 50B2 and 5109 that contain normal calls, like those around 4000. GRAPH_EXEC, PARSER_EXEC, and IO_EXEC are also normal calls. 

===51F3 to 52E8===
This has code that has something to do with something, maybe parsing/handling/executing nostub assembly? 

===52E9 to 7FFF===
This part only has FF FF FF FF FF ... until the end (7FFF).