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     USER DEFINED GRAPHICS
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     The character definer can be run from CP/M by first running the
     UDG.COM program - type in UDG - then loading BASIC - BASIC.COM is on
     your CP/M System disc.

     At the ok prompt type in RUN"UDG"

     After a short introduction the program initialises itself and
     presents you with a list of options. All the options are explained
     quite fully and should be easy to understand.

     The program presents the user with 8 choices (9 if you include QUIT
     to CPM) these include editing a single character or a group of
     characters, saving and loading unfinished character sets and finally
     the piece of resistance;  the SAVE AS COM option. 
     
     For those interested in machine code, basically it writes its own
     little relocation program and looks a bit like this:-

	org	256		or 100H if you prefer
	ld	hl,TEMP 	Start of temp storage area
	ld	de,57900	Where I want it to go, (top memory)
	ld	bc,2100 	Length of program and char data
	ldir			Shift the whole lot
	jp	57900		Now jump to the real program

TEMP	equ	$		The real prog should be at 57900 now
				along with the char data at 58000

	ld	hl,(1)		Get address of JMP blocks
	ld	bc,87		Offset
	add	hl,bc		Calculate address to call
	ld	(CALLAD+1),hl	Stick result into callad+1
	ld	bc,LOCATE	The program CALLS BC, kind of anyway
CALLAD	call	00000		First call above calculation
	defw	233
	ret			Will ret to CPM here

LOCATE				This is called from above routine, The RAM
				holding the Char data is now paged in
	ld	hl,58000
	ld	de,47104	Address of CPM char set
	ld	bc,250*8	250 characters, eight bytes each
	ldir			Put the whole lot on top of the CPM set
	ret			Ret to above routine, After the DEFW.

     John Stevenson.

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     [C] ADVANTAGE 1987