Motorola MC14497P Datasheet

MC14497MOTOROLA

   

The M C14497 is a P CM remote c ontrol transmitter realized in C MOS technology. Using a dual–single (FSK/AM) frequency bi–phase modulation, the transmitter is designed to work with the MC3373 receiver. Information on the MC3373 can be found in the Motorola

Linear

and

Interface Integrated Circuits

book (DL128/D).

There is not a d ecoder device w hich is compatible with the MC14497. Typically, the decoding resides in MCU software.

• Both FSK/AM Modulation Selectable

• 62 Channels (Up to 62 Keys)

• Reference Oscillator Controlled by Inexpensive Ceramic Resonator:

Maximum Frequency = 500 kHz

• Very Low Duty Cycle

• Very Low Standby Current: 50 µA Maximum

• Infrared Transmission

• Selectable Start–Bit Polarity (AM Only)

• Shifted Key Mode Available

• Wide Operating Voltage Range: 4 to 10 V

• See Application Notes AN1016 and AN1203

BLOCK DIAGRAM

ENCODER

7–BIT

SEQUENCE

CONTROL

3–BIT

LATCH

OUTPUT

CONTROL

DIVIDER

10/12

MUX

SCANNER

DIVIDER

OSC

STANDBY

7 6 5 4

FK3

FK1

A4 A3 A2 A1

IN OUT

12 13

500 kHz CERAMIC

RESONATOR

KEYBOARD

Order this document

by MC14497/D



SEMICONDUCTOR TECHNICAL DATA



P SUFFIX

PLASTIC DIP

CASE 707

ORDERING INFORMATION

MC14497P Plastic DIP

PIN ASSIGNMENT

SIGNAL OUT

A4 E5

OSC

out

E614

 Motorola, Inc. 1995

SAME AS IN DL136/D R3

MC14497 MOTOROLA 2

MAXIMUM RATINGS (Voltages referenced to V

)

Parameter

Symbol

Value

Unit

DC Supply Voltage V

– 0.5 to + 18 V

Input Voltage, All Inputs V

– 0.5 to VDD + 0.5 V DC Current Drain per Pin I 10 mA Operating Temperature Range T

– 40 to + 85 °C

Storage Temperature Range T

stg

– 65 to + 150 °C

ELECTRICAL CHARACTERISTICS (T

= 0 to 70°C; all Voltages Referenced to VSS)

Characteristic

Symbol V

Min Max Unit

Supply Voltage V

— 4.0 10.0 V

Supply Current

Idle Operation

10 10

— —

µA

Output Current — Signal

VOH = 3.0 V Source VOL = 0.5 V Sink

4 4

– 900

120

— —

µA

Output Current — Scanner

VOH = 3.0 V Source VOL = 0.5 V Sink

4 4

– 30

245

— —

µA

Output Current — Oscillator

VOH = 3.0 V Source VOL = 0.5 V Sink

4 4

– 300

245

— —

µA

Input Current — Oscillator

Operation Idle, VIL = 0.5 V

± 2

± 80

—

µA

Input Current — Encoder

VIH = 9.0 V VIL = 0.5 V

– 15

—

– 60

µA

Input Voltage — Encoder V

10 10

4 4

—

1.2 —

1.0

This device contains circuitry to protect the inputs against damage due to high static voltages or electric fields; however, it is advised that normal precautions be taken to avoid application of any voltage higher than maximum rated voltages to this high–impedance circuit. For proper operation it is recommended that Vin and V

out

be constrained to the range

VSS ≤ (Vin or V

out

) ≤ VDD.

MC14497MOTOROLA

CIRCUIT OPERATION

The transmitter sends a 6–bit, labelled A (LSB) to F (MSB), binary code giving a total of 64 possible combinations or code words. All of these channels are user selectable, except the last two (where channel 63 is not sent while channel 62 is automatically sent by the transmitter at the end of each transmission as an “End of Transmission” code).

In either mode, FSK or AM, the transmitted signal is in the form of a bi–phase pulse code modulation (PCM) signal. The AM coding is shown in Figure 1.

BIT–n

“0”

“1”

Figure 1. AM Coding

In the AM mode, f1 is a train of pulses at the modulating frequency of 31.25 kHz for a reference frequency of 500 kHz.

In the FSK mode, two modulating frequencies are used as shown in Figure 2.

BIT–n

“0”

“1”

Figure 2. FSK Coding

FSK

In this mode, f3 is 50 kHz and f2 is 41.66 kHz for a reference frequency of 500 kHz.

The keyboard can be a simple switch matrix using no external diodes, connected to the four scanner inputs (A1 – A4) and the eight row input (E1 – E8). Under these conditions, only the first 32 code words are available since bit–F is always at logical 0. However, a simple 2–pole changeover switch, in the manner of a typewriter “shift” key (switch FK3 in the Block Diagram) can be used to change the polarity of bit–F to give access to the next full set of 32 instructions.

An alternative method of accessing more than 32 instructions is by the use of external diodes between the address inputs (see Figure 3). These have the effect of producing “phantom” address inputs by pulling two inputs low at the same time, which causes bit–F to go high (i.e., to logical 1). By interconnecting only certain address inputs it is possible

to make an intermediate keyboard with between 32 and 64 keys.

The other two switches in the Block Diagram (FK1 and FK2) change the modulation mode. Closing FK1 changes the modulation from FSK to AM and the start–bit polarity. Closing FK2 changes the start–bit to a logical 0.

The full range of options available is illustrated in Table 1.

Table 1.

Start

Bit

Modulation Bit–F Channels

E9 = Open 1 FSK 0 0 – 31 E9 = A1 (FK1) 1 AM 0 0 – 31 E9 = A2 (FK2) 0 FSK 0

0 – 31*

E9 = A3 (FK3) 1 FSK 1 32 – 61 E9 = A1 • A2 0 AM 0 0 – 31 E9 = A1 • A3 1 AM 1 32 – 61 E9 = A2 • A3 0 FSK 1

32 – 61*

E9 = A1 • A2 • A3 0 AM 1 32 – 61

*Not allowed.

One of the transmitter’s major features is its low power consumption (in the order of 10 µA in the idle state). For this reason, the battery is perpetually in circuit. It has in fact been found that a light discharge current is beneficial to battery life.

In its active state, the transmitter efficiency is increased by the use of a low duty cycle which is less than 2.5% for the modulating pulse trains.

While no key is pressed, the circuit is in its idle state and the reference oscillator is stopped. Also, the eight address input lines are held high through internal pull–up resistors.

As soon as a key is pressed, this takes the appropriate address line low, signaling to the circuit that a key has been selected. The oscillator is now enabled. If the key is released before the code word has been sent, the circuit returns to its idle state. T o account for accidental activation of the transmitter, the circuit has a built–in reactive time of approximately 20 ms, which also overcomes contact bounce. After this delay, the code word will be sent and repeated at 90 ms intervals for as long as the key is pressed. As soon as the key is released, the circuit automatically sends channel 62, the “End of Transmission” (EOT) code. The transmitter then returns to its idle state.

The differences between the two modulation modes are illustrated in Figure 4. However, it should be noted that in the AM mode, each transmitted word is preceded by a burst of pulses lasting 512 µs. This is used to set up the AGC loop in the receiver’s preamp. In the FSK mode, the first frequency of the first bit is extended by 1.5 ms and the AGC burst is suppressed. In either mode, it is assumed that the normal start–bit is present.

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