;**********************************************************************
;* Filename:	table.asm
;* Project:		EPROM emulator
;* Date:		05 June 2005
;* Version:		0.1
;* Author:		Philip Pemberton
;* 
;* Data table handling code.
;**********************************************************************

	include	"config.inc"		; Device configuration

;**********************************************************************
;** HEADERS
;**********************************************************************

;**********************************************************************
;** CONSTANTS
;**********************************************************************

lbank		equ		0	;register bank for the local state of this module
lbankadr	equ		bankadr(lbank)	;address within local state register bank

;**********************************************************************
;** RAM VARIABLES
;**********************************************************************

; Global state.
	defram	gbankadr
	global	table_High, table_Low
table_High	res		1				; Table high address
table_Low	res		1				; Table low address

; Local state
	defram	lbankadr

;**********************************************************************
;** SUBROUTINES
;**********************************************************************
.table		CODE				; Code segment

;----------------------------------
; Subroutine:	table_Get
; Inputs:
;	W			=	Offset in table
;	table_High	=	Table high address byte (HIGH table)
;	table_Low	=	Table low address byte (LOW table)
; Outputs:
;	W			=	Data byte from table
;	PCLATH set appropriately
; Function:
;	Calculates the offset values for a table lookup. Tables can be anywhere
;	in program memory. Returns with W=offset, and PCLATH set correctly.
;
	glbsub	table_Get
	dbankif	gbankadr
	addwf	table_Low,		F		; 8-bit add operation
	movf	table_High,		W		; Get high 5 bits of address
	skpnc							; Page crossed?
	addlw	D'1'					; Yes, so increment the high byte
	dbankif	PCLATH
	movwf	PCLATH					; Load high address into latch
	dbankif	gbankadr
	movf	table_Low,		W		; Load computed offset into W
	dbankif	PCL
	movwf	PCL						; Call the table
	leave

	END