Z80-GLUE.PLD

Name     z80-glue;
PartNo   Z80C;
Date     03-Dec-2018;
Revision 05;
Designer Nigel Kendrick;
Company  Techmarque;
Assembly Z80 Computer;
Location TBD;
Device   p22v10;

/* Changes this version */

/* Changed to 22V10 to control I/O port too */


/***** Z80 Address Decoder ******************************
 *                 ______________
 *                |   Z80_Glue   |
 *       mreq x---|1  I        24|---x Vcc
 *       iorq x---|2  I      O 23|---x portin
 *         rd x---|3  I      O 22|---x iowr
 *         wr x---|4  I      O 21|---x iord
 *         a3 x---|5  I      O 20|---x memwr
 *         a4 x---|6  I      O 19|---x memrd
 *         a5 x---|7  I      O 18|---x ramrom
 *      a6/a7 x---|8  I      O 17|---x rom
 *         M1 x---|9  I      O 16|---x sio
 *        a14 x---|10 I      O 15|---x ide
 *        a15 x---|11 I      O 14|---x portout
 *        GND x---|12 I      I 13|---x romdis
 *                |____22V10_____|
 */
/********************************************************/
/* This device generates chip select signals for Grant  */
/* Searle's Z80 design                                  */
/* See:http://searle.hostei.com/grant/cpm/index.html    */
/* and https://github.com/linker3000/Z80-Board          */
/********************************************************/

/** Inputs **/
PIN 1		= mreq;		/* Z80 MREQ (active low) */
PIN 2		= iorq;		/* Z80 IORQ (active low) */
PIN 3		= rd;		   	/* Z80 rd (active low)   */
PIN 4		= wr;			/* Z80 wr (active low)   */
PIN 5		= a3;                 
PIN 6		= a4;
PIN 7		= a5;
PIN 8		= a67;			/* A6 and A7 through diode OR */
PIN 9		= m1;
PIN 10		= a14;
PIN 11		= a15;
PIN 13		= romdis;		/* ROM disabled signal */

/** Outputs **/
PIN 23        = !portrd;		/* 8-bit input port               */		
PIN 22		= iowr;		/* io write mode (active low)  	*/
PIN 21		= iord;		/* io read mode (active low)    	*/
PIN 20 	= memwr;		/* mem write mode (active low)  	*/
PIN 19		= memrd;		/* mem read mode (active low)   	*/
PIN 18 	= ramrom;		/* hi = ram, lo = rom operation  	*/
PIN 17 	= rom;			/* disable rom signal 	     	*/
PIN 16		= !sio;		/* sio selected (00-07 active low)	*/
PIN 15 	= !ide;		/* ide selected (10-17 active low)	*/
PIN 14        = !portwr;		/* LEDs and digital inputs */

/** Logic Equations **/
iowr		= iorq # wr;
iord 		= iorq # rd;
memwr		= mreq # wr;
memrd		= mreq # rd;

ramrom		= (a14 # a15) # romdis; 

rom		= !(!a67 &  a5 &  a4 &  a3) # iowr;          /* 38-3F */
sio		=   !a67 & !a5 & !a4 & !a3; 		    /* 00-07 */
portwr		=   !a67 & !a5 & !a4 &  a3 & !iowr & m1;  /* 08-0F */
portrd		=   !a67 & !a5 & !a4 &  a3 & !iord & m1;  /* 08-0F */
/* ide		=   !a67 & !a5 &  a4 & !a3;	*/		   /* 10-17 */
ide		=   !a67 & !a5 &  a4 & !a3 & m1;