Name      23009C6;

Assembly  0001;
Revision  1.0;
PartNo    E81 82S100;
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 }; */

/*
 * 23009C6 is an 82S100, programmed to decode RBM and LBM IOTs to get an address for
 * the Break Map, as stored in E82.
 * An 82S100 has 16 dedicated inputs, and 8 dedicated outputs.  In this case, the inputs
 * are a copy of the AC at the start of the instruction, and the control signals for LBM
 * and RBM.  The outputs are the 4 bit break map address, a signam that indicates an LBM
 * or RBM instruction is in progress, and 2 bits of data for the break map, in the case 
 * of an LBM.
*/

/*
 * The 82S100 is a tri-state device, if CE is inactive, the 
 * outputs are undriven.
*/
Pin 19 = !CE;
/*
 * These are just bits of the AC before the instruction.
*/
Pin [24..27,2..9] = [AC0..11];
/*
 * BTS4 indicates the data is stable and it is time to do our thing.
*/
Pin  21 = BTS4;
/*
 * LBM or RBM is asserted when our IOTs are in progress.
*/
Pin 22 = !RBM;
Pin 23 = !LBM;

/* Outputs */
Pin [10,11,12,13] = [a0..3]; /* E82 */
Pin [15,16] = [d0..1]; /* E82 */
Pin 17 = !lbm_or_rbm;

/*
 * Drive the address to E82.
*/
[a0..3] = [AC6..9];
/*
 * Drive the data to E82.
*/
[d0..1] = [AC10..11];
/*
 * RD2 is set to "b" if this is RACB, otherwise cleared.
*/
lbm_or_rbm = BTS4 & (LBM # RBM);

/*
 * Here is where CE is implemented, though it is tied to 
 * ground in practice.
 * BUBBUG: This didn't need a PLA -- what am I missing?
*/
[a0..3,d0..1].oe = CE;