HP-71B CPU frequency? Message #1 Posted by Christoph Giesselink on 20 Feb 2013, 3:31 p.m.
I'm just wondering about the CPU frequency of real HP-71B?
At the 71IDS vol. 3 document in the =RCKBp entry header is a remark: "note: CPU KHZ is usually 650000 to 700000."
But my experiences show a CPU speed below.
The theoretical speed of Emu71/Win with "Authentic Speed" mode activated is 38 * 16384 = 622592 Hz.
But thank goodness the HP-71B ROM has a CPU speed measuring routine inside which is updated at power on/off or after a INIT:1. The clock speed is standing inside the CSPEED variable (5 nibble) at address 2F977.
So we can read the content with
PEEK$("2F977",5)
In the case of Emu71/Win the result is "9A790". This is a hexadecimal number in reverse order and multiplied with 16 you get the clock speed in Hz.
In our Emu71/Win example:
PEEK$("2F977",5) = "9A790"
-> #097A9h * 16 = #097A90h = 621200 Hz
Now to my two real HP71B:
Sn. 2507Axxxxx ROM rev. 1BBBB:
PEEK$("2F977",5) = "9E990"
-> #099E9h * 16 = #099E90h = 630416 Hz
Sn. 2506Axxxxx ROM rev. 1BBBB:
PEEK$("2F977",5) = "16790"
-> #09761h * 16 = #097610h = 620048 Hz
We see that the results of the real calculators are very similar to the Emu71/Win one and far away from the note inside the 71IDS.
I would be glad if some of you could measure the CPU speed in the way like above on your own HP-71B and post the result here.
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