C8051F38B-GMR View Datasheet(PDF) - Silicon Laboratories

Part Name

Description

Manufacturer

C8051F38B-GMR

Full Speed USB Flash MCU Family

Silicon Laboratories 

C8051F380/1/2/3/4/5/6/7/C

27.3.4. 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 out-

put is toggled. The frequency of the square wave is then defined by Equation 27.1.

FCEXn = -2---------P----FC----P-A---C--0---AC-----P----H-----n--

Note: A value of 0x00 in the PCA0CPHn register is equal to 256 for this equation.

Equation 27.1. Square Wave Frequency Output

Where FPCA 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 PCA 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 reg-

ister. Note that the MATn bit should normally be set to 0 in this mode. If the MATn bit is set to 1, the CCFn

flag for the channel will be set when the 16-bit PCA0 counter and the 16-bit capture/compare register for

the channel are equal.

Write to

PCA0CPLn

0

Reset

ENB

Write to

PCA0CPHn ENB

1

PCA0CPMn

PECCMT PE

WC A A A O WC

MO P P T GMC

1 MPN n n n F

6nnn

n

n

x 000

x

PCA0CPLn

Enable

8-bit

Comparator

8-bit Adder

PCA0CPHn

Adder

Enable

Toggle

match

TOGn

0 CEXn Crossbar

1

Port I/O

PCA Timebase

PCA0L

Figure 27.7. PCA Frequency Output Mode

Rev. 1.4

305

Share Link: