P87LPC779FDH datasheet(48/74 Pages) PHILIPS

48 / 74 page

Philips Semiconductors

P87LPC779

CMOS single-chip 8-bit microcontroller

Product data

Rev. 02 — 03 May 2004

48 of 74

9397 750 13213

8.15.7

Using Timer1 to generate baud rates

When Timer1 is used as the baud rate generator, the baud rates in Modes 1 and 3

are determined by the Timer1 overﬂow rate and the value of SMOD1. The Timer1

interrupt should be disabled in this application. The Timer itself can be conﬁgured for

either ‘timer’ or ‘counter’ operation, and in any of its 3 running modes. In the most

typical applications, it is conﬁgured for ‘timer’ operation, in the auto-reload mode (high

nibble of TMOD = 0010b). In that case the baud rate is given by the formula:

(5)

Tables 39 and 40 list various commonly used baud rates and how they can be

obtained using Timer1 as the baud rate generator.

Mode 1, 3 baud rate

CPU clock frequency / 192 (or 96 if SMOD 1 = 1)

256

TH 1

()

–

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

Table 39:

Baud rates, timer values, and CPU clock frequencies for SMOD1 = 0

Timer Count

Baud Rate

2400

4800

9600

19.2 k

38.4 k

57.6 k

−1

0.4608

0.9216

* 1.8432

* 3.6864

* 7.3728

* 11.0592

−2

0.9216

1.8432

* 3.6864

* 7.3728

* 14.7456

−3

1.3824

2.7648

5.5296

* 11.0592

−4

* 1.8432

* 3.6864

* 7.3728

* 14.7456

−5

2.3040

4.6080

9.2160

* 18.4320

−6

2.7648

5.5296

* 11.0592

−7

3.2256

6.4512

12.9024

−8

* 3.6864

* 7.3728

* 14.7456

−9

4.1472

8.2944

16.5888

−10

4.6080

9.2160

* 18.4320

Table 40:

Baud rates, timer values, and CPU clock frequencies for SMOD1 = 1

Timer Value

Baud Rate

2400

4800

9600

19.2 k

38.4 k

57.6 k

115.2 k

−1

0.2304

0.4608

0.9216

* 1.8432

* 3.6864

5.5296

* 11.0592

−2

0.4608

0.9216

* 1.8432

* 3.6864

* 7.3728

* 11.0592

−3

0.6912

1.3824

2.7648

5.5296

* 11.0592

16.5888

−4

0.9216

* 1.8432

* 3.6864

* 7.3728

* 14.7456

−5

1.1520

2.3040

4.6080

9.2160

* 18.4320

−6

1.3824

2.7648

5.5296

* 11.0592

−7

1.6128

3.2256

6.4512

12.9024

−8

* 1.8432

* 3.6864

* 7.3728

* 14.7456

−9

2.0736

4.1472

8.2944

16.5888

−10

2.3040

4.6080

9.2160

* 18.4320

−11

2.5344

5.0688

10.1376

−12

2.7648

5.5296

* 11.0592

−13

2.9952

5.9904

11.9808

−14

3.2256

6.4512

12.9024

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