Name      23442A2;

Assembly  0001;
Revision  1.0;
PartNo    E87,E113 74S287;
Device    f1508ispplcc84;

Company   None;
Designer  Digital Equipment Corporation;
Location  None;
Date      March 2018;

property ATMEL { jtag=on };
PROPERTY ATMEL { preassign keep };
PROPERTY ATMEL { TMS_pullup=on };
PROPERTY ATMEL { TDI_pullup=on };
/* PROPERTY ATMEL { pin_keep OFF }; */
/* PROPERTY ATMEL { open_collector = INT_RQST }; */

/*
 * 23442A2 is a 74S287, programmed to add three bit numbers.
 * An 74S287 has 8 address inputs, 2 enables, and 4 data outputs.  In this 
 * case, the inputs indicate 3 bits of both operands, a carry input, and an 
 * enable.  If this enable is inactive, the operand on [7,6,5] appears unchanged 
 * at the output.
 * The output bits are the 3 bit sum, and a carry out.
*/

/*
 * The 74S287 is a tri-state device, if either enable is inactive, the 
 * outputs are undriven.
*/
Pin 14 = !G2;
Pin 13 = !G1;
/*
 * These are the bits we need to decide which bank to use.
*/
Pin 15 = add; /* Enable the addition */
Pin  1 = CI; /* Carry in */
Pin  [2,3,4] = [R0..2];
Pin  [7,6,5] = [A0..2];
/*
 * The outputs.
*/
Pin  9 = co; /* Carry out */
Pin [10,11,12] = [s0..2];

/*
 * Perform the addition.
*/
[B0..2] = add & [R0..2];
s2 = CI $ A2 $ B2;
C2 = CI & (A2 # B2)
   # A2 & B2;
s1 = C2 $ A1 $ B1;
C1 = C2 & (A1 # B1)
   # A1 & B1;
s0 = C1 $ A0 $ B0;
co = C1 & (A0 # B0)
   # A0 & B0;

/*
 * Here is where G1 and G2 are implemented.
*/
co.oe = G1 & G2;
[s0..2].oe = G1 & G2;