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RXD-315-KH Datasheet(PDF) 4 Page - List of Unclassifed Manufacturers |
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RXD-315-KH Datasheet(HTML) 4 Page - List of Unclassifed Manufacturers |
4 / 11 page Page 7 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 10µF tantalum capacitor from VCC to ground will help in cases where the quality 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 wired permanently to VCC and transmission controlled by switching VCC to the 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 up to 59,049 (310) unique transmitter-receiver relationships. Tri-state means that 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 |
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