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Page 6

POWER SUPPLY REQUIREMENTS

The module does not have an internal voltage

regulator; therefore it requires a clean, well-regulated

power source. While it is preferable to power the unit

from a battery, it can also be operated from a power

supply as long as noise is less than 20mV. Power

supply noise can affect the transmitter modulation;

therefore, providing a clean power supply for the

module should be a high priority during design.

A 10

Ω resistor in series with the supply followed by a

of supply power is poor. These values may need to be adjusted depending on

the noise present on the supply line.

DATA INPUTS

When the Transmit Enable (TE) line goes high, the states of the eight data input

lines are recorded and encoded for transmission. The data lines are tri-state,

which means that they can be high, low, or floating, though the decoder will

interpret the floating state as a low. This feature means that the data lines do not

require pull-up or pull-down resistors. The states of the data lines can be set by

switches, jumpers, microcontrollers, or hardwired on the PCB.

The encoder will send the states of the address and data lines three times. If the

TE line is still high, it will begin the cycle again. This means that the states of the

data lines are refreshed with each cycle, so the data lines can be changed

without having to pull TE low. There can be up to a 150mS lag in response as

the transmitter finishes one cycle then refreshes and starts over.

ENABLING TRANSMISSION

The module’s Transmit Enable (TE) line controls transmission status. When

taken high, the module initiates transmission, which continues until the line is

pulled low or power to the module is removed. In some cases this line will be

module. This is particularly useful in applications where the module powers up

and sends a transmission only when a button is pressed on the remote.

USING LADJ

The LADJ line allows the transmitter’s output power to be easily adjusted for

range control, lower power consumption, or to meet legal requirements. This is

done by placing a resistor between GND and LADJ. When LADJ is connected

directly to GND, the output power will be at its maximum. Placing a resistor will

lower the output power by up to 7dB, as shown on Page 3 of this data guide.

This is very useful during FCC testing to compensate for antenna gain or other

product-specific issues that may cause the output power to exceed legal limits.

A variable resistor can be used so that the test lab can precicely adjust the output

power to the maximun level allowed by law. The resistor’s value can be noted

and a fixed resistor substituted for final testing. Even in designs where

attenuation is not anticipated, it is a good idea to place a resistor pad connected

to LADJ and GND so that it can be used if needed.

10

Ω

10

μF

Vcc IN

Vcc TO

MODULE

Figure 10: Supply Filter

ENCODER OPERATION

The KH Series transmitter internally utilizes

the HT640 encoder from Holtek. The

encoder begins a three-word transmission

cycle when the Transmission Enable line

(TE) is pulled high. This cycle will repeat

itself for as long as the TE line is held high.

Once TE falls low, the encoder output

completes its final cycle and then stops as

shown in the Encoder / Decoder Timing

diagram. When a transmission enable signal

is applied, the encoder scans and transmits

the status of the 10 bits of the address code

and the 8 bits of the data serially in the order

A0 to A9, D0 to D7.

The status of each address / data pin can be

individually preset to logic high, low, or

floating. The floating state on the data input

is interpreted as logic low by the decoders

since the decoder output only has two

states. The address pins are usually set to

transmit particular security codes by DIP

switches or PCB wiring, while the data is

selected using push buttons or electronic

switches. The floating state allows the KH transmitter to be used without pull-up

or pull-down resistors on the data and address input lines.

SETTING THE TRANSMITTER ADDRESS

The module provides ten tri-state address lines. This allows for the formation of

the address lines have three distinct states: high, low, or floating. These pins

may be hardwired or configured via a microprocessor, DIP switch, or jumpers.

The receiver’s address line states must match the transmitter’s exactly for a

transmission to be recognized. If the transmitted address does not match the

receiver’s local address, then the receiver will take no action.

Power On

Standby Mode

Transmission

Enabled?

Yes

No

3 Data Words

Transmitted

Transmission

Still Enabled?

3 Data Words

Transmitted

Continuously

No

Yes

Figure 8: Encoder Flowchart

Check

Check

< 1 Word

3 Words

Transmitted Continuously

3 Words

1/2 Clock Time

Decoder

Data Out

Decoder VT

Encoder

Data Out

Encoder

Transmit

Enable

1/2 Clock Time

2 Words

2

14

Clocks

2

14

Clocks

Figure 9: Encoder / Decoder Timing Diagram