PCA84C822AP データシートの表示（PDF） - Philips Electronics

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PCA84C822AP

8-bit microcontrollers for remote control transmitters

Philips Electronics 

Philips Semiconductors

8-bit microcontrollers for

remote control transmitters

15 APPLICATION INFORMATION

Product specification

PCA84C122; 222; 422; 622; 822

100 Ω

P00

V DD

P01

P02

XTAL1

P03

P04

XTAL2

P05

P06

T0 / INT

P07

84C122A T1

P10

P11

P12

27 mA

P13

OUT

P14

P15

RESET

P16

P17

VSS

3.0 V

MCD252

Fig.12 PCA84C122A Remote control transmitter application.

Figure 12 shows the main application of the PCA84C122

as a remote control transmitter. Each key of the transmitter

keypad represents a specific command. The keys are in an

orderly matrix with each key connected between an I/O

line of Port 0 and an I/O line of Port 1.

The lines of Port 0 are designated ‘scan’ (output) lines, and

the lines of Port 1 are ‘sense’ (input) lines.

By making each scan line a logic 0 in turn, and each time

looking at the sense lines, the depressed key is detected.

The corresponding command code is determined by using

a software look-up table. This code together with the

system address is sent according to a coding scheme or

protocol (e.g. RC-5). The pulses that are generated are

available at the OUT pin. This pin drives the output

transistor, which provides the current for the IR-LED.

T0/INT is not used and therefore connected to VDD. T1 is

used for system or option selection, therefore a jumper can

be connected to VDD or ground.

When more options must be selected, this can be done in

different ways as illustrated in the following two examples:

1. When the number of keys is sufficiently low a scan line

can be spared. This scan line may be used to connect

a jumper wire to one of the sense lines. Normally the

scan line should be logic 1. When this line is set to

logic 0 the option setting can be read from the sense

lines.

2. By connecting diodes between one sense line and a

number of scan lines (see Fig.12). If necessary these

diodes can be placed parallel to the keys. When the

sense line is set to logic 0 (acts as scan line), the

option setting can be read from the scan lines (which

act as sense lines and should be set to logic 1

beforehand).

For the oscillator a crystal or ceramic resonator may be

used. A resistor in series with the supply, limits the reverse

current through the IC in the event of the supply voltage

being reversed (i.e. wrong insertion of batteries).

1995 May 01

14

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