A minor difference between the HP 15c CE and the original HP-15C (and LE)

[J-F Garnier]

(11-07-2023 02:26 AM)brouhaha Wrote:  

(11-06-2023 10:29 AM)Werner Wrote:  That would suggest that the blinking happens on a regular interval (independent of clock speed), and if the operation is too fast, it will be completed before the display can blink.
Since the CE is many times faster still, you probably won't see any blinking for any 'normal' function (not the solve and integrate).

That's exactly right. The blinking is done in the original Voyager hardware by the R2D2 chip, and is free-running. When the microcode sets blink mode, the display goes into whatever phase the hardware blink happens to be at.

The blink effect I was referring to is not related to the hardware blinking problem.
It's the short display off/display on sequence that happens when a key is pressed on the original 15C.
Very likely it is done with the DISOFF/DISTOG opcodes (although I didn't check).

This short blink is very visible on the original 15C, for every pressed key, including multiple key sequences such as "RCL . n" or "RCL DIM A", and was a convenient visual feedback.
On the 15c LE, the blink is much shorter due to the faster CPU but still noticeable, and on the 15c CE this blink effect completely disappeared. Maybe a side effect of some changes in the display management.

J-F