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prod/doc/: cleanup and clarifications after proofreading

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This commit is contained in:
Werner Almesberger
2011-05-29 10:37:17 -03:00
parent 8b26bb7130
commit 46b15effa9
5 changed files with 52 additions and 30 deletions
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prod/doc/analysis.hmac
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@@ -106,7 +106,8 @@ components as shown in this table:
</TABLE>
<P>
Ground can be accessed at the cover of the crystal.
Note that the fiducials are not connected to ground.
Note that the fiducials, while looking like test points,
are not connected to anything.
<P>
This image shows the location of the measurement points:
<P>
@@ -131,7 +132,7 @@ components as shown in this table:
<P>
Ground can be accessed at the cover of the crystal, at the shield of the
USB connector, or at the test point P11.
Note that the fiducials are not connected to ground.
Note that the fiducials are not connected to anything.
<P>
This image shows the location of the measurement points:
<P>
@@ -144,9 +145,15 @@ This image shows the location of the measurement points:
<SECTION ref="clock" title="Clock frequency">
The precision of the crystal oscillator is crucial for
operation. Anomalies are easy to detect with even a low-cost oscilloscope
and pinpoint specific problems and help to select further analysis steps.
<P>
operation. Anomalies are easy to detect with even a low-cost oscilloscope.
This can pinpoint specific problems and help to select further analysis steps.
<!-- ---------------------------------------------------------------------- -->
<SUBSECTION title="Oscillator tolerances">
The crystal used in <B>atben</B> and <B>atusb</B> has a nominal tolerance
of +/&minus; 15 ppm at 22-28 C. Low-cost oscilloscopes typically have a timing
accuracy of
@@ -154,8 +161,12 @@ accuracy of
measuring the clock output with such an instrument. Full-speed USB only
requires an accuracy of +/&minus; 2500 ppm.
We can therefore consider all results within a range of +/&minus; 1000 ppm as
sufficient, and perform more precise measurements by other means. This
sufficient for an initial assessment, and perform more precise measurements
by other means. This
applies to <B>atben</B> as well as to <B>atusb</B>.
<P>
IEEE 802.15.4 requires the transceiver frequency to be accurate
within +/&minus; 40 ppm.
<!-- ---------------------------------------------------------------------- -->
@@ -197,7 +208,7 @@ the right:
The transceiver provides the clock for the microcontroller in <B>atusb</B>.
A clock signal is therefore always available. Immediately after reset,
the transceiver generates a 1 MHz clock. When the microcontrolled comes out
the transceiver generates a 1 MHz clock. When the microcontroller comes out
of reset, it raises the transceiver's clock output to 8 MHz and then
enables USB.
<P>
@@ -222,7 +233,7 @@ filter.
<TR><TD>0.999-1.001 MHz, ~3.3 Vpp<TD>Check presence of firmware; check for
shorts on SPI signals; check connectivity of SPI signals
<TR><TD>7.992-8.008 MHz, ~3.3 Vpp<TD>Perform precision measurement with
atrf-xtal
atrf-xtal (@@@)
<TR><TD>Other<TD>Check voltages; check for contamination around crystal
</TABLE>
<P>