Preliminary C8051F120/1/2/3 C8051F124/5/6/7 - KEMT FEI TUKE

Preliminary
C8051F120/1/2/3
C8051F124/5/6/7
24.2.4. Frequency Output Mode
Frequency Output Mode produces a programmable-frequency square wave on the module’s associated CEXn pin.
The capture/compare module high byte holds the number of PCA clocks to count before the output is toggled. The
frequency of the square wave is then defined by Equation 24.1.
Equation 24.1. Square Wave Frequency Output
F sqr
=
F PCA
----------------------------------------
2 × PCA0CPHn
Where F PCA is the frequency of the clock selected by the CPS2-0 bits in the PCA mode register, PCA0MD. The
lower byte of the capture/compare module is compared to the PCA0 counter low byte; on a match, CEXn is toggled
and the offset held in the high byte is added to the matched value in PCA0CPLn. Frequency Output Mode is enabled
by setting the ECOMn, TOGn, and PWMn bits in the PCA0CPMn register.
Figure 24.7. PCA Frequency Output Mode
PCA0CPMn
P E C C M T P E
W C A A A O W C
M O P P T G M C
1 M P N n n n F
6 n n n n
n
0 0 0 0 1 0
Enable
PCA0CPLn
8-bit
Comparator
match
8-bit Adder
Adder
Enable
Toggle
TOGn
0
1
PCA0CPHn
CEXn
Crossbar
Port I/O
PCA Timebase
PCA0L
© 2002 Cygnal Integrated Products, Inc. DS008-0.8-AUG02 Page 297