Post Reply 
Benchmarks 71B versus 48GX
06-21-2020, 04:45 PM (This post was last modified: 06-23-2020 06:23 PM by Jonathan Busby.)
Post: #35
RE: Benchmarks 71B versus 48GX
(05-04-2014 10:56 PM)Christoph Giesselink Wrote:  
(05-03-2014 01:57 AM)Mark Hardman Wrote:  HP-28C
1LK7 Saturn CPU (1 MHz)

Sorry, this is wrong. The HP-28C use the same LC frequency generator like in the HP-71B, so the CPU strobe frequency is 600-650 KHz. You can peek the 5 nibble =CSPEED content (#4F00Fh) on a HP-28C with an external peek program. The 5 nibble content is the CPU strobe frequency divided by 16. So a content of #09C05h mean: #09C05h -> #39941d * 16 = #639056d -> ~640 KHz.

If the value present at =CSPEED is generated in a similar fashion to how the value for the entry of the same name on the HP48 is generated, then some corrections are in order. First, on the HP48 series, =CSPEED is generated using the =clkspd routine ( which of course attempts to measure the CPU clock speed ) which is not very accurate, even if display refresh and keyboard scanning are turned off. Secondly, the HP48 series calculators' 32768Hz crystal oscillator seems to vary frequently and the LC circuit that's part of the PLL ( and which uses the crystal oscillator as a reference ) that generates the HFO ( High Frequency Oscillator, which on the HP48G/G+/GX is around ~7.34MHz to ~7.86MHz ) is also subject to frequent variation. So, although the nominal clock speed of the HP-28C may be 640kHz, it may possibly be higher or lower by a non-negligible amount probably due to similar variations in frequency that cause the HP48 series calculators' clock speed to vary, although I believe the variation to be small and on the order of ±20kHz ( ie. it's not so variable that the clock speed would be off by ~360kHz Smile I'd imagine that would have been caught early in the design phase as it would have made the chip unstable Smile ).

In summary, I think that the value stored at "=CSPEED" is not the most reliable indicator of the true clock speed, although I may be wrong though if the HP-28C hardware and its equivalent to the HP48 series "=clkspd" routine differ in some certain crucial aspects Smile

(05-03-2014 01:57 AM)Mark Hardman Wrote:  HP-48GX
Yorke (00048-80063, 160 pin QFP), 4 MHz

This is also a mistake. Only very early HP48G Series calculators had a strobe frequency of 4 MHz. The frequency was then reduced to a nominal speed of ~3.68 MHz.

Well, this is not quite 100% accurate. On the HP48 series, taking the HP48G/G+/GX as an example, the clock speed is derived from the aforementioned HFO divided by 2. AFAIK, the nominal clock speed is around either ~3.93MHz or ~3.67MHz, but, due to reasons I've already mentioned, can vary to a non-negligible degree. I have several HP48GXs that have ~3.9MHz+ clock speeds, and, it seems to me that the "nominal" clock speed is around a little below ~4MHz for these. Also, these calculators are *not* "very early" models Smile ( I've measured ~3.9MHz+ clock speeds on HP48GXs manufactured in Singapore, China and Indonesia Smile )



( NOTE : Edited this post to fix typos : "Hz" -> "kHz")

Aeternitas modo est. Longa non est, paene nil.
Find all posts by this user
Quote this message in a reply
Post Reply 

Messages In This Thread
RE: Benchmarks 71B versus 48GX - Jonathan Busby - 06-21-2020 04:45 PM
RE: Benchmarks 71B versus 48GX - RMollov - 06-22-2020, 04:48 AM
RE: Benchmarks 71B versus 48GX - KimH - 06-17-2020, 11:43 AM
RE: Benchmarks 71B versus 48GX - KimH - 06-17-2020, 12:25 PM
RE: Benchmarks 71B versus 48GX - KimH - 06-17-2020, 02:12 PM
RE: Benchmarks 71B versus 48GX - KimH - 06-18-2020, 06:09 AM
RE: Benchmarks 71B versus 48GX - KimH - 06-18-2020, 07:08 AM
RE: Benchmarks 71B versus 48GX - HP67 - 05-05-2014, 01:42 PM
RE: Benchmarks 71B versus 48GX - rprosperi - 06-17-2020, 10:23 PM
RE: Benchmarks 71B versus 48GX - KimH - 06-19-2020, 04:40 PM

User(s) browsing this thread: 1 Guest(s)