Simple-Computer/ROM.abl at master · mluzarow/Simple-Computer · GitHub

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MODULE ROM

TITLE  'ROM'


DECLARATIONS

" Input pins
A0   pin   2;  " address bus
A1   pin   3;
A2   pin   4;
A3   pin   5;
!MRD pin  11;  " memory read enable (active low)
!NO, !NC pin;

" Output pins
D0   pin 12 istype 'com';  " data bus
D1   pin 13 istype 'com';
D2   pin 14 istype 'com';
BS   pin    istype 'com'; " bounceless switch

TRUTH_TABLE ([A3,A2,A1,A0]->[D2,D1,D0])
             [ 0, 0, 0, 0]->[ 0, 0, 0];   "IN
             [ 0, 0, 0, 1]->[ 0, 0, 1];   "OUT
             [ 0, 0, 1, 0]->[ 0, 1, 1];   "ANA
             [ 0, 0, 1, 1]->[ 0, 0, 1];   "OUT
             [ 0, 1, 0, 0]->[ 0, 1, 0];   "ORA
             [ 0, 1, 0, 1]->[ 0, 0, 1];   "OUT
             [ 0, 1, 1, 0]->[ 0, 0, 0];   "IN
             [ 0, 1, 1, 1]->[ 0, 0, 1];   "OUT
             [ 1, 0, 0, 0]->[ 1, 0, 1];   "ROR
             [ 1, 0, 0, 1]->[ 0, 0, 1];   "OUT
             [ 1, 0, 1, 0]->[ 1, 0, 0];   "ROL
             [ 1, 0, 1, 1]->[ 0, 0, 1];   "OUT
             [ 1, 1, 0, 0]->[ 1, 1, 1];   "ASR
             [ 1, 1, 0, 1]->[ 0, 0, 1];   "OUT
             [ 1, 1, 1, 0]->[ 1, 1, 0];   "ASL
             [ 1, 1, 1, 1]->[ 0, 0, 1];   "OUT

EQUATIONS

BS = NO # !NC & BS; " Bounceless switch
[D0..D2].OE = MRD;

EN