HP-20B key matrix


Appears to be a 6 row (rows are inputs) by 7 column (outputs) matrix, so it could have had up to 42 keys. The on key appears to be outside the matrix. (Pressing the on key takes TP11 to ground.)


Row 0 input is pin PC19

Row 1 input is pin PC20

Row 2 input is pin PC21

Row 3 input is pin PC22

Row 4 input is pin PC23

Row 5 input is pin PC2


Column 0 output is pin PC24

Column 1 output is pin PC25

Column 2 output is pin PC26

Column 3 output is pin PC27

Column 4 output is pin PC28

Column 5 output is pin PC29

Column 6 output is pin PC30

The matrix layout is pretty much what you'd expect, but with the rows running vertically and the columns running across the keypad. I've worked through it and can provide details if needed.

Couple of weird things.

1: PC30 is not listed as a valid I/O pin in my Atmel databook. Maybe it's not bonded out on the BGA or LQFP, but is present on the CoB variant used in the HP-20B?

2: I'm a bit surprised that the on key isn't using one of the wakeup inputs. (I'm sure that design choice will make more sense once I dig into the power management.)

Oh, it appears that bank A and B GPIO (50 pins total) are dedicated to the LCD column and segment drive.

Guess I need to find the analog inputs.



since all ports are both input/outputs, rows and columns can be exchanged, so there is no 'row' 'column' like they were on the saturn.

you got pretty much all the port wrong.. sorry.

the ON key is on a wakup pin: the FWUP (of Fast Wakeup pin)...

regards, cyrille



you got pretty much all the port wrong.. sorry.

Really? Weird, I even double checked my work on that one. I wonder...oh crap. I'll bet I forgot to switch to little endian mode. (OCD Commander likes to boot in big endian, even for ARM targets.) Grrr.

Sorry for the noise guys, I'll rework it tonight.

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