Bugs in Commodore calculators

From: Marko Mäkelä (marko.makela_at_hut.fi)
Date: 2002-10-09 10:37:10

Yesterday I finally tested my 110-volt Commodores with a 50 watt
220->110 volt transformer: the US*1, the 207, the 202 and the SP9000.

The 207 is a stripped-down version of the 202.  It doesn't have a brake
lever for stopping the motor after an operation is completed, and it has
two digits less precision than the 202 and a smaller and less powerful motor.
It was equipped with a black ribbon, and I didn't try it with a black&red
ribbon, but I think it should be able to print negative numbers in red, just
like the 202 does.  I found three bugs in these calculators:

- there is no overflow check (well, I didn't expect that)
- the "× REPT" key does not add up negative numbers
- the CLR or CLEAR key for cancelling an entry prints a "-" sign at the
  right margin if the running total is negative (normally it does not
  print anything)

The US*1 has a more amusing bug.  Once it is powered up, typing K ÷ (the
key labelled "K" and the key labelled with the division operator) will
start an infinite calculation that is constantly updated on the screen.
Sometimes, this loop cannot be broken with the C key: the calculator has
to be switched off.  You can also type a number before typing K ÷.  Then
the display will show parts of the number together with the sequence.
I guess that it's somehow trying to divide by zero.  This calculator
lacks overflow and underflow checks as well.  If I remember correctly,
the only IC inside this calculator has not been made by Commodore or MOS.
So, the calculator might be from the early 1970s.  The display has orange
digits and no lenses like some later LED-based models.

I didn't play much with the SuperPET, as it was overloading and overheating
the transformer.  According to a power meter, it consumed over 70 watts,
which is well over the 50 watt rating of the transformer.  The US*1
consumes about four watts (or five when displaying all 8's), and the 202
(which has a slightly more powerful motor than the 207) took 51 watts when
the REPT key was being pressed down and the motor was running constantly.


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