; U12  PIN Declarations related to address decoding
;
pin	1	 E
pin	3	 A15
pin	4	 A14
pin	5	 A11
pin	7	 A13
pin	8	 A12
pin	9	 RW

pin	12	 CSROM
pin	15	 CSRAM
pin	17	 CSEXT
pin	18	 CSEE
pin	19	 C2000

Logic equations related to address decoding for the BUFFALO monitor:

; $2800-$2FFF (pin 40 of P4, /CS of EXT I/O)
/CSEXT=  /A15 * /A14 * A13 * /A12 * A11;


; $2000-$27FF (U6, 68B50)
/C2000=  /A15 * /A14 * A13 * /A12 * /A11;


;$3000-$7FFF (U4, 28C256)
/CSEE =  /A15 * /A14 * A13 * A12 +
         /A15 * A14;


;$E000-$FFFF (U5, 27C256)
/CSROM  = A15 * A14 * A13;

		
;$8000-$DFFF (U3, 62256)
/CSRAM = A15 * /A14 +
	 A15 *  A14 * /A13;


Logic equations related to address decoding  for the Wytec monitor:
; $2800-$2FFF (pin 40 of P4, /CS of EXT I/O)
/CSEXT=  /A15 * /A14 * A13 * /A12 * A11;

; $2000-$27FF (U6 68B50)
/C2000=  /A15 * /A14 * A13 * /A12 * /A11;

;$3000-$7FFF (U4, 28C256)
/CSEE =  /A15 * /A14 * A13 * A12 +
                /A15 * A14;

;$0800-$0FFF, $1800-$1FFF (U5, 27C256)
/CSROM  = /A15 * /A14 * /A13 *  A11;

;$8000-$FFFF (U3, 62256)
/CSRAM = A15;


Logic equations related to address decoding for SBC mode:
; $2800-$2FFF (pin 40 of P4, /CS of EXT I/O)
/CSEXT=  /A15 * /A14 * A13 * /A12 * A11;

; $2000-$27FF (U6, 68B50)
/C2000=  /A15 * /A14 * A13 * /A12 * /A11;

;$B000-$FFFF (U4, 28C256)
/CSEE =  A15 * /A14 * A13 * A12 +
                A15 * A14;
 
;$0800-$0FFF, $1800-$1FFF (U5, 27C256)
/CSROM  = /A15 * /A14 * /A13 *  A11;

;$8000-$AFFF (U3, 62256)
/CSRAM = A15 * /A14 * /A13 +
	 A15 * /A14 *  A13 * /A12;


Note:

The E and R/W signals are available on U12, so the /CSEXT can be qualified 
by them to control a 74HC244 as an input port or a 74HC574 as an output port.  
We did not use them to generate the /CSEXT because someone may want to use 
the /CSEXT to interface a RAM chip.

To make a 74HC244 as an input port, the logic equation of reading address location $2800 should be:
/RD244=  E * RW * /A15 * /A14 * A13 * /A12 * A11;

To make a 74HC574 as an output port, the logic equation of writing address location of $2800 should be:
 /WR574=  E * /RW * /A15 * /A14 * A13 * /A12 * A11;