PIC16F1508TESSQTO datasheet(289/384 Pages) MICROCHIP

289 / 384 page

 2011 Microchip Technology Inc.

Preliminary

DS41609A-page 289

PIC16(L)F1508/9

25.1

NCOx OPERATION

The NCOx operates by repeatedly adding a fixed value

to an accumulator. Additions occur at the input clock

rate. The accumulator will overflow with a carry

periodically, which is the raw NCOx output. This

effectively reduces the input clock by the ratio of the

addition value to the maximum accumulator value. See

Equation 25-1.

The NCOx output can be further modified by stretching

the pulse or toggling a flip-flop. The modified NCOx

output is then distributed internally to other peripherals

and optionally output to a pin. The accumulator overflow

also generates an interrupt.

The NCOx period changes in discrete steps to create an

average frequency. This output depends on the ability of

the receiving circuit (i.e., CWG or external resonant

converter circuitry) to average the NCOx output to

reduce uncertainty.

25.1.1

NCOx CLOCK SOURCES

Clock sources available to the NCOx include:

•HFINTOSC

•FOSC

•LC1OUT

• CLKIN pin

The NCOx clock source is selected by configuring the

NxCKS<2:0> bits in the NCOxCLK register.

25.1.2

ACCUMULATOR

The accumulator is a 20-bit register. Read and write

access to the accumulator is available through three

registers:

• NCOxACCL

• NCOxACCH

• NCOxACCU

25.1.3

ADDER

The NCOx Adder is a full adder, which operates

independently from the system clock. The addition of

the previous result and the increment value replaces

the accumulator value on the rising edge of each input

clock.

25.1.4

INCREMENT REGISTERS

The Increment value is stored in two 8-bit registers

making up a 16-bit increment. In order of LSB to MSB

they are:

• NCOxINCL

• NCOxINCH

Both of the registers are readable and writeable. The

Increment registers are double-buffered to allow for

value changes to be made without first disabling the

NCOx module.

The buffer loads are immediate when the module is dis-

abled. Writing to the NCOxINCH register first is neces-

sary because then the buffer is loaded synchronously

with the NCOx operation after the write is executed on

the NCOxINCL register.

EQUATION 25-1:

Note:

The increment buffer registers are not

user-accessible.

FOVERFLOW

NCO Clock Frequency Increment Value



----------------------------------------------------------------------------------------------------------------

n = Accumulator width in bits

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