HP 35s (and 42s) Crystal replacement



#13

Reacentry I got some cylindrical crystal resonator of 65.536kHz.

Then tried to replace the crystal of the HP 42s and 35s.

Overclocking 42s is successful, however,
hp35s seems strange.

Quote:
I experimentally replaced the original 32.768kHz crystal resonator at X1 with a 65.536kHz one, and found some curiosity.
Doubling the clock frequency would not affect the calculation speed at all.
Though the idle current are increased, the run-time current are almost identical to that of the original (i.e. fclock=32.768kHz).



If the frequency of the crystal does not affect the calculation speed, what is the use of the crystal? What is clocking the MPU, I wonder?

#14

Quote:
Reacentry I got some cylindrical crystal resonator of 65.536kHz.

Then tried to replace the crystal of the HP 42s and 35s.

Overclocking 42s is successful, however,
hp35s seems strange.




If the frequency of the crystal does not affect the calculation speed, what is the use of the crystal? What is clocking the MPU, I wonder?


This has been answered in previous threads.
The 32.768KHz watch crystal in the 35S is only for the Real Time Clock (RTC) function. The main oscillator is an RC type, the frequency of which is set by a single external resistor (internal capacitor).

The main oscillator frequency can also be software controlled with various divider ratios. So there will be a register in the processor somewhere where you could also change the frequency.

Check the Sunplus processor datasheet for details.

Dave.


#15

Quote:
This has been answered in previous threads.
The 32.768KHz watch crystal in the 35S is only for the Real Time Clock (RTC) function.

Thanks DaveJ



Would you tell me which is that thread please, and how can I use the RTC function if it is on the 35s?



Regards, Lyuka


#16

Hi!
I can help you to put another 32K of SRAM in the empty ROM place (used in another models), you can use it for assembly programming. There is some wiring involved, but it is very simple.

Best regards,

Nelson


#17

then if HP 42S uses or has sam hardware as 17BII then it is possible to upgrade 17BII to 32K?

thanks


#18

Hi,
I tried this, but the 17B's firmware doesn't recognize past 8KB of SRAM. Only 42S have this possibility.

Best regards,

Nelson

Edited: 8 Jan 2008, 12:44 p.m.

#19

What RTC functions are available on the HP 35s? I've never seen any description of this facility on the HP 35s.

But then, there aren't *any* detailed official HP descriptions of HP35S functions available on HP web sites. I wonder why, after all the months that the HP 35s has been out, there is still no manual for the HP 35s available for download.

Mike
(HP calc user since 1977, definitely not impressed by the HP 35s)


#20

In the 35s, the RTC oscillator is used for display refresh and keyboard scanning.


#21

Thank you.

I've been a bit confused by the word 'RTC'.

I confirmed that the cursor blinking interval and the PSE time have been halved by this crystal replacement.

These function on the 35s should better be said as an interval timer.

IMHO the 'Real Time Clock' generally means what maintains the real time and date information.



Regards, Lyuka


#22

Quote:
Thank you.

I've been a bit confused by the word 'RTC'.

I confirmed that the cursor blinking interval and the PSE time have been halved by this crystal replacement.

These function on the 35s should better be said as an interval timer.

IMHO the 'Real Time Clock' generally means what maintains the real time and date information.



Regards, Lyuka


The Sunplus micro does not appear to have a hardware RTCC in it, but the external low power crystal is designed primarily to implement an RTCC in software. But you can also use it for other things as HP have done in this case.

See:
Sunplus

Dave.


Edited: 9 Jan 2008, 4:18 a.m.


#23

Thanks DaveJ

I've got the data sheet of the GPLB31A and confirmed its block diagram.

Lyuka

#24

With setting the speed register at 0x40300 to 0xF by using the built-in debugger,

this modified 42s was able to execute a user program without error at quadruple speed of the original 42s.

The power supply current while executing a program, was increased from 3.3mA to 7.6mA.

Power supply current (fclock=65.536kHz, *(0x40300)==0xF, Vbattery=4.71V(SR44~3), Ta=23‹C)
Irun = 7.6mA
Iidle = 480ƒÊA(typ.)

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