Name      23441A2;

Assembly  0001;
Revision  1.0;
PartNo    E74 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 }; */

/*
 * 23441A2 is a 74S287, programmed to decode current conditions and decide
 * whether to use IB, DB, Bank 0, or the Bank Map.
 * An 74S287 has 8 address inputs, 2 enables, and 4 data outputs.  In this 
 * case, the inputs indicate which conditions are happening that might affect
 * the current bank in use.
*/

/*
 * 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 = !INT_IN_PROG; /* Interrupts force bank 0 */
Pin  1 = DFEN; /* DF should be used for the MB access */
Pin  2 = !INIT_EN; /* Reset forces bank 0 */
Pin  3 = !BCPMAD; /* Non CPU Cycle */
Pin  4 = TS4; /* Time State 4 */
Pin  7 = PAUSE; /* IOT in progress */
Pin  6 = EBM; /* The Break Map is enabled. */
Pin  5 = !LBM_OR_RBM; /* Break Map IOT */
/*
 * The outputs.
*/
Pin  9 = !force0; /* Force 0 into the bank value. */
Pin 10 = !bmen; /* The Break Map supplies the bank value. */
Pin 11 = !dbs; /* The currend DB is needed. */
Pin 12 = !ibs; /* The current IB is needed. */

/*
 * Resets and interrupts force bank zero.
*/
force0 = INT_IN_PROG # INIT_EN;
/*
 * Use the Break Map if it is enabled and this didn't come from the CPU.
 * BUGBUG: How are PAUSE, TS4 and LBM_OR_RBM used?
*/
bmen = EBM & BCPMAD;
/*
 * Use DB when we are using DF.
*/
dbs = DFEN;
/*
 * Default to use IB.
*/
ibs = !dbs & !bmen & !force0;

/*
 * Here is where G1 and G2 are implemented.
*/
force0.oe = G1 & G2;
bmen.oe = G1 & G2;
dbs.oe = G1 & G2;
ibs.oe = G1 & G2;