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Glolab GL-104 Encoder / Decoder

The Glolab GL-104 microprocessor based Encoder / Decoder is designed for use with wireless modules, infrared remote controls and other devices that operate with serial input and output data. It can be used as either an encoder or a decoder by simply connecting pin 7 either high for an encoder or low for a decoder. It can encode or decode four bits of data and four address bits (16 addresses).

When used as an encoder, one of two Input modes can be selected by connecting pin 8 either high or low. In one mode the encoding of data can be active high initiated by a transmit enable pin and in another mode the encoding can be active low initiated by any or all data pins. When used as a decoder, either momentary or latched data outputs can be selected by connecting pin 12 either high or low. A momentary valid transmit output indicates when valid data is being received.

When not encoding or decoding, the GL-104 remains in a low power mode where it draws only 1 microampere making it ideal for battery powered applications. It is powered by 5 volts and draws about 3.5 milliamperes not including loads, when active.   As an encoder it becomes active when triggered by transmit enable or data input. As a decoder it becomes active when it receives serial data.

gl-104-4.jpg (31344 bytes)

An internal clock is generated by a 4 MHz ceramic resonator connected to pins 15 and 16 which provides accurate frequency control and therefore better serial data synchronization than the resistor controlled oscillators used in some encoders and decoders. This allows higher speed data transfer without the risk of lost data. A resonator of the type that has three pins and contains internal capacitors to minimize components is recommended for oscillator frequency control. 4 MHz Resonators are available from Digi-Key, ECS p/n X902, Panasonic p/n PX400 and Mouser, ECS p/n 520-ZTT400MG and from Glolab p/n CR4.

The GL-104 can be powered with 5 volts from a battery or other power source. For completely fail safe operation under all conditions, a voltage detector reset (VDR) circuit that produces a brownout reset should be used. This guards against loss of memory data or unpredictable operation in a case where the power supply voltage momentarily drops, but not low enough to produce an internal power on reset. A 4.7K to 10K resistor connected from +5 volts to pin 4 may be used in place of a VDR if brownout reset is not required. These circuits are available in a TO92 package from Digi-Key, Microchip p/n MCP100-450DI/TO and Mouser, Seiko p/n 628-80840CLY and from Glolab p/n VDR. The VDR circuits use only 1 microampere of operating current.

One GL-104, one CR4 and one VDR are required for each encoder application. Another GL-104 , CR4 and VDR are required for each decoder application.

TRANSMITTER

Figure 5 shows a basic wireless RF transmitter application circuit with the GL-104 used as an encoder.

gl-104-5.jpg (27011 bytes)

The four address pins can be connected to Vss or Vdd through switches or can be hard wired, they cannot be left floating.

Two different input modes are selectable by connecting pin 8 to either Vss or Vdd. The Vss connection causes the transmit enable and all four data in pins to be active high. In this mode a high level must be placed on the transmit enable pin to initiate a transmit sequence and a high level on the data pins will produce a high level on the serial output pin that drives an RF module or infrared LED. Transmit enable and data in pins cannot be floating. They are usually driven by logic or other circuits in this mode.

When pin 8 is connected to Vdd the transmit enable and all data in pins are pulled up to Vdd by internal 200 microampere current sources and they become active low. In this mode a low level on either the transmit enable or on any or all data in pins will initiate a transmit sequence and will produce a high level on the serial output. The internal pullups in combination with active low and transmit-initiate for each data in pin is convenient for use with push button switch inputs.

The serial output generated at pin 9 when a transmit sequence is initiated consists of three bytes. The first byte contains a fixed set of address bits, the second byte contains the address bits that have been selected by the encoder address pins and the third byte contains the four data bits. These three bytes are automatically sent at least three times (one packet) when a transmit sequence is started regardless of how short a time transmit is enabled in either active high or active low mode. Transmission of packets will repeat as long as transmit is enabled. A packet is sent in 20 milliseconds.

RECEIVER

Figure 6 shows a basic wireless receiver application circuit with the GL-104 used as a decoder.

gl-104-6.jpg (24862 bytes)

Latched outputs can be selected by connecting pin 12 to Vdd either directly or through a resistor. By connecting it through a resistor, the outputs can be reset by connecting pin 12 to Vss through a push button switch. Momentary outputs are selected by wiring pin 12 directly to Vss.

The packets of serial output generated by the transmitter encoder and sent to the receiver decoder by wireless, infra red or other means are fed into serial input pin 13 of the decoder. A packet is stored and the address bytes within it are compared with  those of the decoder address pin settings. If  the addresses match then the data is passed to the output pins. Each of the output pins can both source and sink 25 milliamperes.

View some application schematics.

DOWNLOAD a GL-104 data manual including application circuits, in PDF format

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