; JED2EQN -- JEDEC file to Boolean Equations disassembler (Version V063)
; Copyright (c) National Semiconductor Corporation 1990-1993
; Disassembled from 00437.jed. Date: 2024-02-22
;
;
; The RAM chip VCC is driven from the battery and the system VCC via diode.
; RAM CS is pulled high to RAM VCC when the system is unpowered. 
;

chip 00437 GAL22V10

RNW	= 1 

i2	= 2 

BS	= 3 
BA	= 4 
A12	= 5 
A15	= 6 
E	= 7 ; from JK FF via 50R resistor
A14	= 8 
A13	= 9 
A11	= 10 
EN	= 11 

GND	= 12 

A10	= 13 

/RAM_EN_Q1	= 17 ; to RAM /CS pin 20 via transistor and pull-up to Vbatt.

/IO_EN	= 20	; to pin 4 of the 74LS138
/ROM_CS	= 21	; direct to chip

/freemem	= 15 
/intack	= 16 


/o18	= 18 
/o19	= 19 
/o22	= 22 

VCC	= 24 

@ues ffffffffffffffff

equations

; intermediates

io_space	= /A15 * /A14 *  A13 * /A12 * /A11 * /A10	; 02800 hex

;
;
; The io enable signal goes to a 74LS138 one-of-eight decoder
; that decodes A5,4,3 into 8 eight-byte I/O chip select signals.
;
; /0 = U25        /CS, 6821 Parallel I/O
;
; /2 = U18 pin 13 /CS, 6840 Programmable Timer Module
; /3 = U4  pin 9  /CS, IEEE488 Talker/Listener
; /4 = U24        /CS, 6821 Parallel I/O
;
;
;
eight_k_block_0	= /A15 * /A14 * /A13	; 0000 to 1FFF hex

reading		= RNW

; pins

o22		= i2 * E * ROM_CS
		+ i2 * E * RAM_EN_Q1 * EN
;
; The ROM addressing explains why
; there are many vectors to 3000h
; at the end of ROM. 
;
;

ROM_CS		= reading *  A15			; above 8000h
		+ reading * /A15 *  A14			; above 4000h
		+ reading * /A15 * /A14 *  A13 *  A12	; above 3000h


IO_EN		= EN * io_space 

o19		= EN * io_space * i2

o18		= /i2
		+ EN *  io_space

;
; BS * /BA = interrupt or reset acknowledge
; valid on the leading edge of Q
;

intack		= BS * /BA * E

RAM_EN_Q1	= EN * eight_k_block_0 
;
; freemem when not ROM or I/O:
;
freemem		= /ROM_CS * /IO_EN * /RAM_EN_Q1

/IO_EN.oe	= EN
/o19.oe 	= EN
/o18.oe 	= EN
/RAM_EN_Q1.oe	= EN

/o22.oe		= vcc
/ROM_CS.oe	= vcc
/intack.oe	= vcc
/freemem.oe 	= vcc