On Wed, Nov 4, 2009 at 4:34 AM, William Case <billlinux@xxxxxxxxxx> wrote:
> Hi;
>
> I have the 102 page Intel Data Sheet in front of me. I am trying to
> determine the High and Low voltage numbers for transistors on my
> system.
>
> I am not trying to do anything mysterious or build a CPU in my garage.
> I am just doing a small write up for myself that has an introductory
> paragraph for a section on how DRAM memory works that says something
> like "My machine's CPU and Memory transistors typically use XXX volts
> when thrust High and XXX volts when driven Low." I understand that
> things can get more complex, but I am only trying to establish a sense
> or feel of what is happening inside, not write a technical manual for
> engineers.
>
> All the various Vtt, Vcc, Vss, VID etc. are getting confusing. I will
> either have to spend a couple of days googling trying to interpret the
> Data Sheet or take a short cut by asking here.
>
> What designation or parameters should I be looking at for high and low
> voltage (logical/binary 1 and logical/binary 0)?
>
> I am using the Intel 318732.pdf {Core 2 Duo Processor Data Sheet}.
Somewhat off topic for this list ..
I have no expertise in this but out of curiousity I had a look at the
datasheet. My conclusions are below.
No doubt there will be others here with greater expertise who are
welcome to correct any errors.
Reference: http://download.intel.com/design/processor/datashts/318732.pdf
The intent of the datasheet is to describes its interfaces, not its
internal operation.
1) Table 2: the processor outputs a byte that controls the regulator
to provide it a supply voltage VCC in the range 0.5 to 1.6 V.
2) Table 4 Note 7: VTT is the databus (frontside bus FSB) fixed
reference voltage. It does not vary.
3) Table 3: VTT absmax = 1.45V
4) Table 4: VTT typical = 1.2V
5) Section 2.7: The databus uses GTL+. The "0 or 1" reference
threshold for input voltages is GTLREF which is derived from VTT by a
simple resistive divider.
6) Table 15: With resistors 57.6 and 100 ohm: GTLREF=VTT*100/(57.6+100)=0.76V
7) So for the databus:
Table 11: (approx) 0 < VIL < GTLREF (VIL = voltage detected as 0 =
below 0.76V)
Table 11: (approx) GTLREF < VIH < VTT (VIH = voltage detected as 1 =
above 0.76V)
Table 11: (approx) VOH = VTT (VOH = voltage output for 1 = 1.2V)
I could not see any VOL (voltage output for 0) for the FSB in this datasheet.
8) Table 12 and Table 13 specify open-drain and cmos interfaces which
use different voltages.
Background docs:
http://en.wikipedia.org/wiki/Gunning_Transceiver_Logic
http://focus.ti.com/lit/an/scea003a/scea003a.pdf (mentions VOL < 0.4V for GTL+)
Hope this is useful.
David
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