メガドライブの検討 - AVR編

  • PORT A:D0-D7
  • PORT B:D8-D15
  • PORT C
    • 0: Address Latch A1-A7, A8-15 (to 74574 x2)
    • 1: Address Latch A16-A23 (to 74574)
    • 2: /C_OE
    • 3: /C_CE
    • 4: /LO_MEM
    • 5: /AS
    • 6: /LDSW
    • 7: /UDSW
  • PORTD
    • 0: /CART_IN
    • 2: USB D+
    • 4: USB D-

残りは空き。 /AS がでてるのは救いだが、 R/W がでてないのがちょっとな...

address の latch は下記。

HC574_1_D[8:1] = cartridge_data[7:0];
HC574_1_CLK = portd0;
HC574_1_OE = 0;
cartridge_address[7:1] = HC574_1_Q[8:2];

HC574_2_D[8:1] = cartridge_data[15:8];
HC574_2_CLK = portd0;
HC574_2_OE = 0;
cartridge_address[15:8] = HC574_2_Q[8:1];

HC574_3_D[8:1] = cartridge_data[7:0];
HC574_3_CLK = portd1;
HC574_3_OE = 0;
cartridge_address[23:16] = HC574_3_Q[8:1];