HP-45 Question


OK, maybe I'm imagining this but I'm sure I once read an article that said the timer function on the hp-45 was put in by a bored student/intern

I've tried finding the article.

Does anyone else remember this?




Discovered by a bored student/intern, maybe.

I don't see how you could add code into a masked ROM.


--- Les



Dave presumably meant that he'd read that the timer function had been added by a student intern working at HP.

I hadn't heard that. I know one of the guys that worked on the HP-45, so I'll inquire.


Thanks Eric

I'm sure I didnt imagine this story: that there was quite a lot of spare room in the ROM for the 45 so he added a timer function.

I've done the normal google searches of course :)


The code for the timer is already in the rom, they decided not to add the timer at nearly the last minute. The timer would not be so accurate because they did not include the crystal to control the clock speed (system clock)

I think there is a set of three buttons you can press at one time to get it in and out of timer mode though. I just don't remember what they were.


The timer would not be so accurate because they did not include the crystal to control the clock speed (system clock)
IIRC, mine is off by approx. 20%, so *not so accurate* seems to be an euphemism ;-). I don't remember the keys either, but this information is easily found on the net.



Indeed. In this very site, to be exact:


Best regards from V.


A similar story was for an "easter egg" for a ROM for the HP-85. I think someone put in a game. Perhaps this was a student and someone mixed up both features?


My friend, here is quote from this site as how timer work.

The HP-45 had code to implement a timer. This was never exposed as a user feature because the lack of a quartz crystal in the HP-45 made the timer fairly inaccurate. The timer could be invoked by pressing RCL and then pressing CHS 7 8 all at the same time. Once in timer mode, CHS toggled it between running and stopped. Pressing 1-9 stored the current time in that register when the timer was running or recalled the stored time when the timer was stopped. Pressing the decimal point key, brought the calculator back to normal mode with the time still in the display. (Pressing Enter also resumed normal mode but cleared the display.) It's possible to add a crystal to the HP-45.

My 45 prototype comes with a crystal installed - so the timer certainly wasn't a secret feature. It was probably killed by marketing or due to being pointless (what good for is a clock that only runs for a couple of hours until the batteries are down; since the 45 is non-programmable, you cannot do some funky calculations either...)

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