The OpenLib() and ExecLib functions were added in 83+ ROM v2.20 (found only on the 84+/84+ SE).

They are provided so that flash apps can provide functions to BASIC programs.

OpenLib() takes the name of a flash app as its argument. Example OpenLib(MYAPP). It performs a series of complicated checks. The following must be (for simplicity's sake) at 4087h:

DB 96h,0E2h
DW 0100h,label

Then anywhere in the app:


label:
	DW 1
	DB 2
	DB 0
	DW LibraryHook

LibraryHook points to a hook routine. The first byte must be 083h or it will not be valid.

After running OpenLib() a BASIC program can use ExecLib to interface with the app. When ExecLib is parsed, the hook set up is called. There are no register inputs or outputs. Variables such as A-Z and Ans may be used. For example, 5:ExecLib could be a handy way to do this.

The address of the hook is 9B80h, and it is bit 4 of IY+3Eh.