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TXM-315-KH3

KH3 Series Transmitter Module

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Theory of Operation

The KH3 Series transmitter operation is straightforward. When the Transmit

Enable (TE) line is taken high, the on-board encoder IC is activated. The

encoder detects the logic states of the data and address lines. These

states are formatted into a 3-word transmission, which continues until the

TE line is taken low. The encoder creates a serial data packet that is used

to modulate the transmitter.

The transmitter section is based on a simple, but highly-optimized,

architecture that achieves a high fundamental output power with low

harmonic content. This ensures that most approval standards can be

met without external filter components. The KH3 Series transmitter is

exceptionally stable over variations in time, temperature, and physical

shock as a result of the precision SAW device that is incorporated as the

frequency reference.

The transmitted signal may be received by a Linx KH3 Series receiver

/ decoder module or a Linx LR Series receiver combined with the

appropriate decoder IC. Once data is received, it is decoded using a

decoder IC or custom microcontroller. The transmitted address bits are

checked against the address settings of the receiving device. If a match

is confirmed, the decoder’s outputs are set to replicate the transmitter’s

inputs.

Compatibility with the KH2 Series

The Legacy KH2 Series used encoders and decoders for Holtek® and the

KH3 migrates to the Linx DS Series encoder and decoder. The protocol

and functionality are compatible. There is some difference in the hardware

set-up for the address lines and the data lines. The legacy Holtek®

products used tri-state lines, so high, low and floating were each valid

states. The DS Series has bi-state lines; high and low only. Three lines

have been added to the KH3 module to allow for the selection of how the

address and data line states are interpreted. Please see the Input Type

Selection section for more details.

The KH3 transmitter has been designed to be compatible with legacy

systems. The module has been configured for the most common use of the

KH2 so that it can be placed on existing boards without modification. This

makes the KH3 a drop-in replacement for most applications.

–10 –

Encoder Operation

The KH3 Series transmitter internally utilizes

the DS Series encoder. The encoder begins

Power On

a three-word transmission cycle when the

Transmission Enable line (TE) is pulled high.

Standby Mode

This cycle repeats itself for as long as the TE

line is held high. Once TE falls low, the encoder

completes its final cycle and then stops as

No

Transmission

Enabled?

shown in the Encoder / Decoder Timing diagram

Yes

(Figure 16). When a transmission enable signal

is applied, the encoder scans and transmits the

3 Data Words

Transmitted

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.

No

Transmission

Still Enabled?

Yes

The state of address / data pins can be

interpreted as ONE, ZERO or OPEN bits,

following the logic of the D_CFG, A_CFG0 and

3 Data Words

Transmitted

Continuously

A_CFG1 inputs. See the Input Type Selection Figure 16: Encoder Flowchart

section for more details. The open bit 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.

Encoder

Transmit

Enable

Encoder

Data Out

< 1 Word

3 Words

Decoder VT

Decoder

Data Out

2 Words

Check

Figure 17: Encoder / Decoder Timing Diagram

Transmitted Continuously

3 Words

Check

– 11 –

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