Name       Piasw;
Partno     TBD;
Date       03/02/95;
Revision   01;
Designer   Peter;
Company    N/A;
Assembly   Atari800;
Location   Q101;
Device	   p16l8;

/******************************************************************/
/*                                                                */
/* This file contains the logic to handle the PIA switching.      */
/*                                                                */
/*  Removed from 'mapper.pld', since a EP900 is slight overkill   */
/*  for just this function.                                       */
/*                                                                */
/******************************************************************/
/*  Allowable Target Device Types:  PAL16L8                       */
/******************************************************************/

/**  Inputs  **/

Pin 1 = !piaCS;		/* Original CS from decode ($D300-D3FF) */
Pin 2 = A2;		/* Used to select which PIA is in use */
Pin 3 = A0;		/* Used to indicate which port is being accessed */
Pin 4 = CB2_a;		/* CB2 from original PIA */
Pin 5 = CB2_b;		/* CB2 from second PIA */
Pin 6 = !os800;		/* Pull low for 800 OS mode */

/**  Outputs  **/

Pin 13 = !PIA1_cs;	/* Output to original PIA (Joy ports) */
Pin 14 = !PIA2_cs;	/* Output to new PIA (bank switch) */
Pin 15 = CB2_out;	/* The replacement CB2 sig (SIO /command) */

/**  Logic Equations  **/

/* Select the correct CB2 signal, depending on mode */

CB2_out = (CB2_a & os800) # (CB2_b & !os800);

/* Generate the PIA chip selects */

/* This is the on-board PIA */
PIA1_cs = piaCS & ((os800 & !A2) #
	(!os800 & ((A2 & A0) # (!A2 & !A0))));

/* This is the additional PIA */
PIA2_cs = piaCS & ((os800 & A2) #
	(!os800 & ((!A2 & A0) # (A2 & !A0))));