122-32000 Parallax Inc, 122-32000 Datasheet - Page 133

• Manufacturer Part Number: 122-32000
• Description: MANUAL PROPELLER
• Manufacturer: Parallax Inc

Specifications of 122-32000

• Accessory Type: Manual
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With/related Products: Propeller Education (PE) Kit
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

{{ Blinker2.spin }}
CON
<remaining code unchanged>
Here we changed the
the clock mode to use the internal phase-locked loop (PLL) to wind up the XIN frequency by
four times, resulting in a System Clock frequency of 5 MHz * 4 = 20 MHz.
Try compiling and downloading Blinker2 with these settings. You should see the LEDs blink
at a faster rate than you’ve seen before.
NOTE: Since we specified
If we had specified a
calculated an
frequency. This is why it is more common to specify an XIN frequency (
than a clock frequency (
The Clock PLL circuit, when enabled, always winds up the frequency by 16 times, but you
can select any of the 1x, 2x, …16x taps for the final System Clock frequency using the
settings
Try changing
configures the System Clock to be 5 MHz * 16 = 80 MHz! Most of the LEDs blink so
quickly that they appear to be solidly on.
Exercise 10: Clock-Related Timing
The last exercise may have made you aware of something; our Output object is easily
affected by the clock frequency. It relies on a specific, hard-coded time-base but subordinate
objects (those that are not the top object) should never do that because they cannot predict
what the clock frequency will be for the many applications they may be used for.
Additionally, the Propeller application can change the System Clock frequency a number of
times throughout its run time.
Suppose that we really intended to make an Output object that toggles pins at a specific rate
that is essentially clock independent. This means that it must respond dynamically to the
System Clock frequency. Below is the modified code; make sure to edit your code to match.
_CLKMODE = XTAL1 + PLL4X
_XINFREQ = 5_000_000
MAXLEDS = 6
PLL1X
,
_CLKMODE
_XINFREQ
PLL2X
,
_CLKMODE
_CLKFREQ
PLL4X
_CLKFREQ
from
value of 1.25 MHz, which doesn’t match our external crystal’s
_XINFREQ
,
PLL8X
XTAL1 + PLL4x
setting slightly by adding the
value of 5 MHz instead, adding the
).
and
here,
PLL16X
'Set to ext low-speed crystal, 4x PLL
'Frequency on XIN pin is 5 MHz
'Number of LED objects to use
_CLKFREQ
.
to
XTAL1 + PLL16x
is automatically calculated to be 20 MHz.
+ PLL4X
Propeller Manual v1.0 · Page 133
and download again. That
PLL4X
value. This configures
setting would have
_XINFREQ
) rather