; JED2EQN -- JEDEC file to Boolean Equations disassembler (Version V063)
; Copyright (c) National Semiconductor Corporation 1990-1993
; Disassembled from j031-u7.jed.
; Date: 2022-11-04
;
; J031 SGT1 STEbus colour video graphics board
; IC7
; Decodes the MPU memory map.
;
; 2022-11-04 Read and analysed to this first draft.
; To do: compile and check the JED files match originals.
;

chip j031-u7 PAL16L8

A10	=	1	
A11	=	2	
A12	=	3	
A13	=	4	
A14	=	5	
A15	=	6	
E	=	7	
RnW	=	8	
/UNMAP	=	9	
GND	=	10	
/ROM_OE	=	12	; EPROM Output Enable, pin 20 (pin 12 on original diagram is wrong)	
/MRW	=	13	

/BUSRD	=	14	
/VTC	=	15	
/VMR	=	16	
/BUSWR	=	17	
BUS	=	18	; Unknown, not on circuit diagram.	
/ROM_CE	=	19	; EPROM Chip Enable, pin 22 (pin 19 on original diagram is wrong)
VCC	=	20 

RnW	=	8	
/UNMAP	=	9	
GND	=	10	
/OE	=	11	; 

; intermediates:

last_8k		=	A15 * A14 * A13


mem_0000_to_03FF	=	/A15 * /A14 * /A13 * /A12 * /A11 * /A10 ; 1k
mem_0400_to_07FF	=	/A15 * /A14 * /A13 * /A12 * /A11 *  A10 ; 1k
mem_0800_to_0bFF	=	/A15 * /A14 * /A13 * /A12 *  A11 * /A10 ; 1k
mem_0c00_to_0FFF	=	/A15 * /A14 * /A13 * /A12 *  A11 *  A10 ; 1k

read	=	E * RnW
write	=	E * /RnW

equations

ROM_CE	=	E
;
; VTC = Video Timing Controller = the HD6845:
;
VTC	=	E     * mem_0400_to_07FF
;
; STEbus 
;
BUSRD	=	read  * mem_0800_to_0bFF * BUS
BUSWR	=	write * mem_0800_to_0bFF * BUS

MRW	=	write * mem_0c00_to_0FFF

VMR	=	read * /A15 *  A12
	+	read * /A15 *  A13
	+	read * /A15 *  A14
	+	read *  A15 * /A14
	+	read *  A15 *  A14 * /A13
	+	read * UNMAP

ROM_OE	=	read * last_8k * /UNMAP

/ROM_CE.oe	=	vcc
/BUSWR.oe	=	vcc
/VMR.oe		=	vcc
/VTC.oe		=	vcc
/BUSRD.oe	=	vcc
/MRW.oe		=	vcc
/ROM_OE.oe	=	vcc