Prototype RS232 AVR parallel flash programmer

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AVR to Flash interface pinout

The interface on the AVR side consists of

  • 8-bit direct databus
  • 3-bit control bus (CE/OE/WE)
  • 4 line address bus - expands upto 24-bit

Data bus

  • data bits 7..2 = PD7 - PD2
  • data bits 1..0 = PB1 - PB0

Control bus

  •  !CE = PC3
  •  !OE = PC4
  •  !WE = PC5

Address bus

The address bus consists of 3 shift registers (74HC164N) with common clock signal and outputs arranged so that with 1 clock pulse one can set A2..A0 - so with 6 pulses (12 toggles) one can set A17..A0, 8 pulses (maximum) would give A23..A0.

The shift register that outputs
A0,3,6,9,12,15...	A1,4,7,10,13,16...	A2,5,8,11,14,17
is at				
PC1			PC0			PB4

The clock line is PB2 - usage is that you set the bit values to "send", then send a pulse (up+down transitions) on the clock line.