HP 50g and missed keypresses

By | 18 Mar 2017

The default key debouncing wait time in the HP 50g is very long so that it misses lots of keypresses when typing fast. E.g. when typing 500 the calculator only registers 50. This behaviour is controlled by the KEYTIME setting.

The KEYTIME setting specifies the number of processor ticks, any further keypresses are ignored after a key was pressed. The default value is 1138 which resembles about 140 ms.

Setting this to e.g. 500 (~61 ms) makes entering numbers much more reliable. Some users even disabled it by setting it to 0 and had no problems at all.

Changing the value

To set the KEYTIME setting to 500, press the following keys (in RPN mode):

  1. 500
  2. ENTER
  5. STO ▶

But this only works for the current session. After a reboot of the device, the value will be back to the default value of 1138 again.

Changing the value on bootup

To have this value changed on every bootup of the calculator, we have to save the instructions to a special variable called STARTUP. To do this, press the following keys (in RPN mode):

  1. + (this will insert << >> and place the cursor in the middle)
  2. 500
  3. 0 (this will insert a )
  6. ENTER
  8. STO ▶

This stores the instruction into the special variable STARTUP which gets evaluated on every bootup.

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