Prototype RS232 AVR parallel flash programmer
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Hardware description
This device is the workbench using which flashrom's generic serial external programmer protocol code was and will be tested.
Short hardware listing:
- An ATmega88/168 development board
- RS232 level converter
- 5V regulator
- ATmega168
- 18.432MHz
- 16k program memory
- 1k SRAM
- 3 74HC164N shift registers for the address bus
- DIL40 socket for flash to be programmed
- I just happened to have DIL40 socket instead of a DIL32 (it's wired for 32).
AVR to Flash interface pinout
The interface on the AVR side consists of
- 8-bit direct data bus
- 3-bit control bus (CE/OE/WE)
- 4 line address bus — expands up to 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.
