Name     SFD800 ;
PartNo   PAL12L6 ;
Date     20/05/2021 ;
Revision 01 ;
Designer Philip Smart ;
Company  engineers@work ;
Assembly SFD800 ;
Location  ;
Device   g16v8a;

/* *************** INPUT PINS *********************/
PIN  1   = A0                        ; /* Address bus A0                  */ 
PIN  2   = A1                        ; /*             A1                  */ 
PIN  3   = A2                        ; /*             A2                  */ 
PIN  4   = A3                        ; /*             A3                  */ 
PIN  6   = A4                        ; /*             A4                  */ 
PIN  7   = A5                        ; /*             A5                  */ 
PIN  8   = A6                        ; /*             A6                  */ 
PIN  9   = A7                        ; /*             A7                  */ 
PIN 19   = IORQn                     ; /* Z80 IORQ active low             */ 
PIN 11   = WRn                       ; /* Z80 WR active low               */ 
PIN 12   = RDn                       ; /* Z80 RD active low               */ 
PIN 5    = RESET                     ; /* System Reset active high        */ 

/* *************** OUTPUT PINS *********************/
PIN 13   = BUSn                      ; /* BUS direction, low = read into Z80, high = write to FD IC's */ 
PIN 18   = FDCn                      ; /* WD1773 Chip Select active low I/O - Address 0xD8 .. 0xDB */ 
PIN 14   = DRIVEn                    ; /* Disk Drive Select active low - Address 0xDC */ 
PIN 17   = DDENn                     ; /* Drive Density select active low - Address 0xDE */ 
PIN 15   = RESn                      ; /* Peripheral Reset active low */ 
PIN 16   = SIDEn                     ; /* Disk Head Select active low - Address 0xDD */ 

/* Decoder equations. */
FIELD ADDR = [A7..A0];
WD1773SEL  = !IORQn & ADDR:[D8..DB];
SIDESEL    = !IORQn & !WRn & ADDR:[DD..DD];
DRIVESEL   = !IORQn & !WRn & ADDR:[DC..DC];
DDENSEL    = !IORQn & !WRn & ADDR:[DE..DE];  
BUSREAD    = !IORQn & !RDn & ADDR:[D8..DE];

/* Assign output pins based on equations. */
BUSn       = !BUSREAD;
RESn       = !RESET;
FDCn       = !WD1773SEL;
SIDEn      = !SIDESEL;
DRIVEn     = !DRIVESEL;
DDENn      = !DDENSEL;