Datasheet

COP8SGE5, COP8SGE7, COP8SGH5

COP8SGK5, COP8SGR5, COP8SGR7

SNOS516E –JANUARY 2000–REVISED APRIL 2013

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Table 6. Prescaler Factors (continued)

Prescaler Prescaler

Select Factor

11010 13.5

11011 14

11100 14.5

11101 15

11110 15.5

11111 16

As an example, considering Asynchronous Mode and a CKI clock of 4.608 MHz, the prescaler factor selected is:

4.608/1.8432 = 2.5 (1)

The 2.5 entry is available in Table 6. The 1.8432 MHz prescaler output is then used with proper Baud Rate

Divisor (Table 5) to obtain different baud rates. For a baud rate of 19200 e.g., the entry in Table 5 is 5.

N − 1 = 5 (N − 1 is the value from Table 5)

N = 6 (N is the Baud Rate Divisor)

Baud Rate = 1.8432 MHz/(16 × 6) = 19200 (2)

The divide by 16 is performed because in the asynchronous mode, the input frequency to the USART is 16 times

the baud rate. The equation to calculate baud rates is given below.

The actual Baud Rate may be found from:

BR = Fc/(16 × N × P) (3)

Where:

BR is the Baud Rate

Fc is the CKI frequency

N is the Baud Rate Divisor (Table 5).

P is the Prescaler Divide Factor selected by the value in the Prescaler Select Register (Table 6)

NOTE

In the Synchronous Mode, the divisor 16 is replaced by two.

Example:

Asynchronous Mode:

Crystal Frequency = 5 MHz

Desired baud rate = 9600

Using the above equation N × P can be calculated first.

N × P = (5 × 10

)/(16 × 9600) = 32.552 (4)

Now 32.552 is divided by each Prescaler Factor (Table 6) to obtain a value closest to an integer. This factor

happens to be 6.5 (P = 6.5).

N = 32.552/6.5 = 5.008 (N = 5) (5)

The programmed value (from Table 5) should be 4 (N − 1).

Using the above values calculated for N and P:

BR = (5 × 10

)/(16 × 5 × 6.5) = 9615.384 (6)

% error = (9615.385 − 9600)/9600 x 100 = 0.16% (7)

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