; JED2EQN -- JEDEC file to Boolean Equations disassembler (Version V063)
; Copyright (c) National Semiconductor Corporation 1990-1993
; Disassembled from j031-u32.jed.
; Date: 2022-11-04
;
; J031 SGT1 STEbus colour video graphics board
; IC32
; Converts the 4-bit pixel data into RGB signals at TTL levels.
;
; 2022-11-04 Read and analysed to this first draft.
; To do: compile and check the JED files match originals.
;

chip j031-u32 PAL16R6

CLK	=	1	; CY3 inverted

d0	=	2	; shift register nibble
d1	=	3 
d2	=	4 
d3	=	5 

modsel1	=	6 	; mode select
modsel2	=	7 

cy2	=	8	; cycle signal

dispen	=	9	; display enable

GND	=	10 

/OE	=	11	; always grounded

csync	=	12	; composite sync

rf13	=	13	; not on circuit diagram

; RGB are registered outputs: 

red	=	14 

green	=	15

blue	=	16 

; registered function

rf17	=	17	; not on circuit diagram

hsync	=	19	; horizontal sync in

VCC	=	20 

equations

/rf17	:=	         cy2 *  csync * /dispen
	+	/rf17 *  cy2 * /csync
	+	/rf17 * /cy2 *  csync
	+	/rf17 * /cy2 * /csync

rf17.oe	=	OE

/blue	:=	/d2 *  modsel1
	+	/d1 * /modsel1 * /cy2
	+	/d3 * /modsel1 *  cy2
	+	/rf17

blue.oe	=	OE

/green	:=	/d1 *  modsel1
	+	/d1 * /modsel1 * /cy2
	+	/d3 * /modsel1 *  cy2
	+	/rf17

green.oe	=	OE

/red	:=	/d0 *  modsel1
	+	/d0 * /modsel1 * /cy2
	+	/d2 * /modsel1 *  cy2
	+	/rf17

red.oe	=	OE

/rf13	:=	/rf13 * /csync
	+	/rf13 * /cy2
	+	cy2 * csync *  hsync * /modsel2
	+	cy2 * csync * /hsync *  modsel2

rf13.oe =	OE