address decoder for 6502 homebrew computer

address-decoder-16v8-2.pld

Name     address-decoder-16v8-2 ;
PartNo   00 ;
Date     2017-02-05 ;
Revision 01 ;                                                         
Designer Maciej Bartosiak ;
Company  m ;
Assembly None ;
Location  ;
Device   g16v8a;

/* *************** INPUT PINS *********************/
pin	1 = PHI2;	/* clock PHI2 			*/ 
pin	2 = RW;	/* RW signala from 65c02	*/ 
pin	[3..7] = [A15..A11];

/* *************** OUTPUT PINS *********************/
pin	14 = !RAM_1	; /* RAM_1	0000-7FFF	0... .... .... 32K  */
pin	13 = !RAM_2	; /* RAM_2	8000-BFFF	10.. .... .... 16K  */
pin	15 = LCD	; /* LCD	C000-CFFF	1100 .... ....  4K  */
pin	16 = !VIA_1	; /* VIA_1	D000-D7FF	1101 0... ....  2K  */
pin	17 = !VIA_2	; /* VIA_2	D800-DFFF	1101 1... ....  2K. */
pin	18 = !ROM	; /* ROM	E000-FFFF	111. .... ....  8K  */
pin	19 = !OE	;

/* *************** LOGIC ***************************/
OE = RW;

RAM_1	= !A15 & PHI2;
RAM_2	= A15 & !A14 & PHI2;

IO_SP	= A15 &  A14 & !A13;

LCD	= IO_SP  & !A12 & !A11 & PHI2;
VIA_1	= IO_SP  &  A12 & !A11;
VIA_2	= IO_SP  &  A12 &  A11;

ROM	= A15 &  A14 &  A13;