Propeller Manual

_XINFREQ – Spin Language Reference
_XINFREQ
Constant: Pre-defined, one-time settable constant for specifying the external crystal
frequency.
CON
_XINFREQ =
Expression
• Expression is an integer expression that indicates the external crystal frequency; the
frequency on the XI pin. This value is used for application start-up.
Explanation
_XINFREQ specifies the external crystal frequency, which is used along with the clock mode to
determine the System Clock frequency at start-up. It is a pre-defined constant symbol whose
value is determined by the top object file of an application.
_XINFREQ is either set directly by
the application itself, or is set indirectly as the result of the
_CLKMODE and _CLKFREQ settings.
The top object file in an application (the one where compilation starts from) can specify a
setting for
_XINFREQ in its CON block. This, along with the clock mode, defines the frequency
that the System Clock will switch to as soon as the application is booted up and execution
begins.
The application can specify either
_XINFREQ or _CLKFREQ in the CON block; they are mutually
exclusive and the non-specified one is automatically calculated and set as a result of
specifying the other.
The following examples assume that they are contained within the top object file. Any
_XINFREQ settings in child objects are simply ignored by the compiler.
For example:
CON
_CLKMODE = XTAL1 + PLL8X
_XINFREQ = 4_000_000
The first declaration in the above CON block sets the clock mode for an external low-speed
crystal and a Clock PLL multiplier of 8. The second declaration indicates the external crystal
frequency is 4 MHz, which means the System Clock’s frequency will be 32 MHz because 4
MHz * 8 = 32 MHz. The
_CLKFREQ value is automatically set to 32 MHz because of these
declarations.
Page 236 · Propeller Manual v1.1