In SX Microcontrollers, SX/B Compiler and SX-Key Tool, peterverkaik wrote:

Hi Bean,

I am also working on a Sx48 protoboard addon using a 32K sram.
It is possible to use only 24 pins on the sram when you also have
an I2C bus. I use the SCL line also as OE for the sram. (sram CS = GND)
Port C = sram DQ0-DQ7
Port D = sram A0-A7
Port E = sram A8-A14, WE
Port A = SCL,SDA,TX0,RX0
Port B = application (in attachement is layout example of quad birectional uart).
That would give you 5 free I/O pins for the buttons.

For single switches with a common ground you could also use a resistor ladder
where each button results in a different R value, and then use RC time.

You could also connect 1k resistors (or resistor network) to DQ0-DQ7 and
the buttons to these resistors, so that when a button is closed, it pulls
a DQ line low (sram OE must be high during button scan).

regards peter

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