/* iot2.pld - SBC6120 Model 2 I/O Decode GAL #2				*/
/*									*/
/*   Copyright (C) 2001 by Robert Armstrong, Milpitas, California.	*/
/*									*/
/*  This program is free software; you can redistribute it and/or	*/
/* modify it under the terms of the GNU General Public License as	*/
/* published by the Free Software Foundation; either version 2 of the	*/
/* License, or (at your option) any later version.			*/
/*									*/
/*  This program is distributed in the hope that it will be useful, but	*/
/* WITHOUT ANY WARRANTY; without even the implied warranty of		*/
/* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU	*/
/* General Public License for more details.				*/
/*									*/
/*   You should have received a copy of the GNU General Public License	*/
/* along with this program; if not, write to the Free Software		*/
/* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111 USA.	*/
NAME		IOT2;
PARTNO		IOT2;
REVISION	2;
DATE		06/05/01;
DESIGNER	Robert Armstrong;
COMPANY		Spare Time Gizmos;
ASSEMBLY	SBC6120;
LOCATION	U11;
DEVICE		G22V10;
                                                    
/* INPUTS...								*/
Pin 1  = GROUP_2_IOT;		/* IOT in progress (from IOT GAL #1) 	*/
Pin 2  = GROUP_1_IOT;		/*  "   "    "       "    "   "   "	*/
Pin [3..5] = [MA9..MA11];	/* IOT function code			*/
Pin 6  = !WRITE;		/* HD6120 WRITE strobe			*/
Pin 7  = !READ;			/*    "   READ strobe			*/
Pin 8  = !IOCLR;		/*    "   I/O CLEAR			*/
Pin 10 = KEYBOARD_FLAG;		/* console keyboard flag		*/
Pin 11 = PRINTER_FLAG;		/* console printer flag			*/
Pin 13 = !DASP;			/* IDE drive activity			*/
/* Pin 9 unused */

/* OUTPUTS...								*/
Pin 22 = LOAD_DAR;		/* clock the disk address register	*/
Pin 14 = !READ_KEYBOARD_BUF;	/* enable the keyboard data buffers	*/
Pin 15 = !LOAD_PRINTER_BUF;	/* clock the printer transmit latches	*/
Pin 16 = !CLR_KEYBOARD_FLAG;	/* clear the console keyboard flag	*/
Pin 21 = !CLR_PRINTER_FLAG;	/* clear the console printer flag	*/
Pin 23 = IOCLR_OUT;		/* an inverted version of IOCLR L	*/
Pin 18 = SKIP;			/* cause an IOT to skip			*/
Pin 19 = INTREQ;		/* request HD6120 interrupt		*/
/* Pin 20 unused */
/* Pin 17 unused */

/* IOT DECODING... 							*/
/*   The IOT GAL #2 doesn't have enough inputs to decode the full nine	*/
/* bit device code (MA3 to MA11), so IOT GAL #1 tells #2 what to do via	*/
/* two control signals, GROUP 1 IOT H and GROUP 2 IOT H.  These signals	*/
/* are outputs of IOT GAL #1 and inputs to IOT GAL #2, and are defined	*/
/* as shown:								*/
/*									*/
/*	G1	G2	IOT
/*	-----	-----	------------------				*/
/*	FALSE	FALSE	idle (no IOT in progress)			*/
/*	TRUE	FALSE	603x (console keyboard)				*/
/*	FALSE	TRUE	604x (console printer)				*/
/*	TRUE	TRUE	641x (system)					*/
IOT_603X = ( GROUP_1_IOT & !GROUP_2_IOT);
IOT_604X = (!GROUP_1_IOT &  GROUP_2_IOT);
IOT_641X = ( GROUP_1_IOT &  GROUP_2_IOT);
$include ..\IOTS.INC


/*   IOCLR_OUT is simply an inverted version of IOCLR. It seems a waste	*/
/* to use a whole PLD just for an inverter, but I didn't have an extra	*/
/* inverter in the design and this PLD had a free output!		*/
IOCLR_OUT = IOCLR;


/* This table pretty much summarizes the console logic:			*/
/*									*/
/*	Signal			IOTs					*/
/*	-----------------	--------------				*/
/*	CLR_PRINTER_FLAG	CAF, TCF, TLS				*/
/*	CLR_KEYBOARD_FLAG	KCC, KRB				*/
/*	READ_KEYBOARD_BUF	KRS, KRB				*/
/*	LOAD_PRINTER_BUF	TPL, TLS				*/
/*									*/
/*   The only thing remotely tricky is that CAF clears the printer flag	*/
/* but it doesn't clear the keyboard flag.  This is the way a real -8	*/
/* works.  Remember that we don't have to deal with asserting C0 or C1 	*/
/* here, since IOT GAL #1 takes care of them.				*/
CLR_PRINTER_FLAG  = IOCLR # (WRITE & (TCF # TLS));
CLR_KEYBOARD_FLAG = WRITE & (KCC # KRB);
READ_KEYBOARD_BUF =  READ & (KRS # KRB);
LOAD_PRINTER_BUF  = WRITE & (TPL # TLS);


/*   This GAL handles all the skip and interrupt logic for the entire	*/
/* SBC6120, including the console terminal.  Right now there's only one	*/
/* other device besides the console that can cause a skip or interrupt,	*/
/* and that's the IDE disk.  Note that the HD6120 samples the SKIP line	*/
/* during the WRITE phase of any IOT cycle, and we have to be careful	*/
/* to assert that signal only then.  INTREQ can, of course, be asserted	*/
/* at any time...							*/
SKIP = WRITE &
	 ((KSF & KEYBOARD_FLAG) # (TSF & PRINTER_FLAG) # (SDRQ & DASP));
INTREQ = KEYBOARD_FLAG # PRINTER_FLAG # DASP;


/* The LDAR IOT loads the AC into the RAM disk address register... */
LOAD_DAR = WRITE & LDAR;