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6. RAM
FIGnition includes 8Kb (or 0.9Mb) of serial RAM storage for running programs; storing
temporary data and maintaining the bitmapped video mode when FIGnition is turned on,
and the contents are lost when the computer is turned off. The chip must operate at no
more than 3.6V and therefore we need to convert between the AVR's 5v signals and the
Serial RAM chip. Random access to Serial RAM is relatively slow and FIGnition's firmware
takes some effort to use it effectively.
6.1 Circuit Diagram
6.2 Operation
6.2.1. Electrical Connections
The Serial RAM is electrically similar to the Flash memory ( see section 5.2.1). It needs a
3.6v power supply and shares most of the same signals and resistors to convert voltages
and transport data between the AVR and itself. There are two differences:
• The Serial RAM needs its own Chip Select pin, which is connected from the AVR's
pin 16 to pin 1 of the serial RAM and requires R... and R... to convert the signal.
• The Serial RAM doesn't have a write-protect pin (FIGnition doesn't use the Flash
chip's write-protect anyway).
6.2.2 The SPI Protocol
Fig 6.1
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