MikroElektronika PIC Microcontrollers PIC18 Uživatelský manuál stáhnout pdf (Strana 14)

and the nominal bit rate (NMR) is

NBR ¼ 1=T

BIT

ð9:2Þ

The time quantum is derived from the oscillator frequency and the programmable

baud rate prescaler, with integer values from 1 to 64. The time quantum can be

expressed as:

¼ 2 ðBRP þ 1Þ=F

OSC

ð9:3Þ

where T

is in ms, F

OSC

is in MHz, and BRP is the baud rate prescaler (0 to 63).

Equation (9.2) can be written as

¼ 2 ðBRP þ 1ÞT

OSC

ð9:4Þ

where T

OSC

is in ms.

An example of the calculation of a nominal bit rate follows.

Example 9.1

Assuming a clock frequency of 20MHz, a baud rate prescaler value of 1, and a

nominal bit time of T

BIT

¼ 8*T

, determine the nominal bit rate.

Solution 9.1

Using equation (9.3),

¼ 2 ð1 þ 1 Þ=20 ¼ 0:2ms

also

BIT

¼ 8  T

¼ 8  0:2 ¼ 1:6ms

From Equation (9.2),

NBR ¼ 1=T

BIT

¼ 1=1:6ms ¼ 625; 000bites=s or 625Kb=s

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MikroElektronika PIC Microcontrollers PIC18 Uživatelský manuál Strana 14