; 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
; IC5
; STEbus interface logic.
;
; 2022-11-04 Read and analysed to this first draft.
; To do: compile and check the JED files match originals.
;

chip j031-u5 PAL16R6

CLK	=	1	; STEbus SYSCLK
/BUSY	=	2	; 
BA0	=	3	; STEbus A0
HEN	=	4	; LK2
HCM	=	5	; STEbus 
BCM0	=	6	; STEbus CM0
/BDATSTB =	7	; STEbus DATSTB*
/ACTIVE	=	8	; MPU status bit
/ADDE	=	9	; STEbus address enable
GND	=	10	; 
/OE	=	11	; tied low
DATACK	=	12	; inverted by TR1 to become DATACK*

rf13	=	13	; Not shown on circuit diagram
rf14	=	14	; Presumably does the job of the 74LS164 in many designs
rf15	=	15	; 
rf16	=	16	; 
rf17	=	17	; 

/BUSDR	=	18	; STEbus Latched Data Read (from IC4, 74LS374)
/BUSST	=	19	; STEbus Status Register Enable (IC6, 74F240)
VCC	=	20	; 

; Intermediate equations

addressed	=	BDATSTB * ADDE

addressed_nHCM	=	addressed * /HCM

equations

BUSST	=	addressed_nHCM * BCM0 *  BA0

BUSDR	:=	addressed_nHCM * BCM0 * /BA0
;
; rf17, 16, 15 are cleared if the address or data strobe or HCM become invalid.
;

/rf17	:=	/ADDE
	+	/BDATSTB
	+	HCM
	+	addressed_nHCM * /rf17 *               /rf14
	+	addressed_nHCM * /rf17 *        /rf15
	+	addressed_nHCM * /rf17 * /rf16
	+	addressed_nHCM *  rf17 *  rf16 * rf15 * rf14
	+	BUSY * /BA0 * HEN * /BCM0

/rf16	:=	/ADDE
	+	/BDATSTB
	+	HCM
	+	addressed_nHCM * /rf16 *        /rf14
	+	addressed_nHCM * /rf16 * /rf15
	+	addressed_nHCM *  rf16 *  rf15 * rf14

/rf15	:=	/ADDE
	+	/BDATSTB
	+	HCM
	+	addressed_nHCM * /rf15 * /rf14
	+	addressed_nHCM *  rf15 *  rf14

/rf14	:=	/ADDE
	+	/BDATSTB
	+	HCM
	+	addressed_nHCM * /BA0 * rf14 * ACTIVE
	+	addressed_nHCM *  BA0 * rf14

/rf13	:=	addressed_nHCM * /BCM0 * /rf17
	+	/BDATSTB * /rf13
	+	rf17 * /rf13
	+	HCM * /rf13
	+	/rf13 * /ADDE


/DATACK	=	addressed_nHCM * /BA0 * ACTIVE

/BUSST.oe	=	vcc
/BUSDR.oe	=	OE
rf17.oe	=	OE
rf16.oe	=	OE
rf15.oe	=	OE
rf14.oe	=	OE
rf13.oe	=	OE
DATACK.oe	=	vcc