Infrared Encoder/Decoder

www.DataSheet4U.com MCP2122 Infrared Encoder/Decoder Features • Pinout compatible with HSDL-7000 • Compliant with IrDA® Standard Physical Layer Specification (version 1.3) • UART to IrDA Standard Encoder/Decoder - Interfaces with IrDA Standard Compliant Transceiver • Baud Rates: - Up to IrDA Standard 115.2 Kbaud Operation • Transmit/Receive Formats (Bit Width) Supported: - 1.63 µs • Low-power Mode (2 µA at 1.8V, +125°C) Package Types PDIP, SOIC 16XCLK TX RX VSS 1 2 3 4 8 7 6 5 VDD TXIR RXIR RESET MCP2122 Block Diagram MCP2122 TX Encode TXIR CMOS Technology • Low-voltage operation • Extended temperature range • Low power consumption RESET Reset Logic Baud Rate Generator Decode RXIR 16XCLK RX IrDA Family Selection Baud Rate Device Host UART IR Encoder / Decoder Yes Yes Yes Yes Yes Protocol Layer Handler No No IrCOMM (3) (3) (3) Clock Source XTAL 16XCLK XTAL XTAL XTAL Host UART Baud Rate Selection HW/SW By 16XCLK None - Fixed HW HW Comment MCP2120 2400 2400 312,500 (1) 312,500 (1) MCP2122 2400 2400 115,200 (1) 115,200 (1) MCP2140 9600 9600 Extended Temperature Range (-40°C to +125°C) MCP2150 9600 9600 115,200 (2) 115,200 (2) MCP2155 9600 9600 115,200 (2) 115,200 (2) IrCOMM IrCOMM Host UART easily interfaces to a PC’s serial port (DTE) Host UART easily interfaces to a modem’s serial port (DCE) Note 1: The host UART and the IR operate at the same baud rates. 2: The host UART and IR baud rates operate independent of each other. 3: Supports the 9-wire “cooked” service class of the IrCOMM Application Layer Protocol.  2004 Microchip Technology Inc. Preliminary DS21894B-page 1 MCP2122 NOTES: DS21894B-page 2 Preliminary  2004 Microchip Technology Inc. MCP2122 1.0 DEVICE OVERVIEW TABLE 1-1: The MCP2122 is a stand-alone IrDA standard encoder/ decoder device that is pinout-compatible with the Agilent® HSDL-7000 encoder/decoder. The MCP2122 has two interfaces: the host UART interface and the IR interface (see Figure 1-1). The host UART interfaces to the UART of the Host Controller. The Host Controller is the device in the embedded system that transmits and receives the data. The IR interface connects to an infrared (IR) optical transceiver circuit that converts electrical pulses into IR light (encode) and converts IR light into electrical pulses (decode). This IR optical transceiver circuit could be either a standard infrared optical transceiver (such as a Vishay® TFDU 4100) or it could be implemented with discrete components. For additional information, please refer to AN243, “Fundamentals of the Infrared Physical Layer” (DS00243). When the Host Controller transmits the UART format data, the MCP2122 receives this UART data and encodes (modulates) it bit by bit. This encoded data is then output as electrical pulses to the IR transceiver. The IR transceiver will then convert these electrical pulses to IR light pulses. The IR transceiver also receives IR light pulses (data), which are outputted as electrical pulses. The MCP2122 decodes (demodulates) these electrical pulses, with the data then being transmitted by the MCP2122 UART. This modulation/demodulation method is performed in accordance with the IrDA standard. Table 1-1 shows an overview of some of the device features. Figure 1-1 shows a typical application block diagram. Table 1-2 shows the pin definitions of the MCP2122 during normal operation. MCP2122 FEATURES OVERVIEW MCP2122 UART, IR 16XCLK Yes 8-pin PDIP 8-pin SOIC Features Serial Communications: Baud Rate Selection: Low-power Mode: Packages: Infrared Technology Features: • Universal standard for connecting portable computing devices • Effortless implementation • Economical alternative to other connectivity solutions • Reliable, high-speed connection • Safe to use in any environment; can even be used during air travel • Eliminates the hassle of cables • Allows PCs and non-PCs to communicate with each other • Enhances mobility by allowing users to easily connect 1.1 Applications Some applications where an IR interface (MCP2122) could be used include: • • • • • • Data-Logging/Data Exchange System Setup System Diagnostic Read Out Manufacturing Configuration Host Controller Firmware Updates System Control FIGURE 1-1: SYSTEM BLOCK DIAGRAM Host Controller PICmicro® MCU Host UART Interface Protocol Handler MCP2122 TX Encode TXIR IR Optical Interface Transceiver TFDU 4100 TXD SO UART SI RESET Clock (I/O) 16XCLK RX Decode Reset Logic Clock Logic RXIR RXD  2004 Microchip Technology Inc. Preliminary DS21894B-page 3 MCP2122 TABLE 1-2: Pin Name 16XCLK TX RX VSS RESET PIN DESCRIPTION Pin Number PDIP 1 2 3 4 5 SOIC 1 2 3 4 5 Pin Type I I O — I Buffer Type ST ST — P ST Description 16x external clock source input Asynchronous receive from Host Controller UART Asynchronous transmit to Host Controller UART Ground reference for logic and I/O pins Resets the Device H = Normal Operation L = Device in Reset Asynchronous receive from infrared transceiver Asynchronous transmit to infrared transceiver Positive supply for logic and I/O pins RXIR TXIR VDD Legend: ST I P O 6 7 8 = = = = 6 7 8 I O — ST — P Schmitt Trigger input with CMOS levels Input Power Output DS21894B-page 4 Preliminary  2004 Microchip Technology Inc. MCP2122 2.0 DEVICE OPERATION TABLE 2-1: Input Pin Name RESET State L The MCP2122 is a low-cost infrared encoder/decoder. The baud rate is the same for the host UART and IR interfaces and is determined by the frequency of the 16XCLK signal, with a maximum baud rate of 115.2 Kbaud. The MCP2122 is made up of these functional modules: • Clock Driver (16XCLK) • Reset • IR Encoder/Decoder - IrDA Standard Encoder - IrDA Standard Decoder The 16XCLK circuit allows a clock input to provide the device clock. The Reset circuit supports an external reset signal. The IR Encoder logic takes a data bit and converts it to the IrDA standard signal according to the IrDA standard Physical Layer specification, while the IR Decoder logic takes the IrDA standard signal and converts it to 8-bit data bytes. DEFAULT OUTPUT PIN STATES IN DEVICE RESET Output Pin State RX H TXIR L Device in Reset mode Comments TABLE 2-2: DEFAULT OUTPUT PIN STATES AFTER DEVICE RESET (RESET = L→H) Output Pin State RX — TXIR L→H After 7 - 8 16XCLK →L pulses, the TXIR pin will pulse high. L — — After 4 16XCLK pulses, RX = L. Comments Input Pin Name State TX L H RXIR L H — H→L H 2.1 Power-up As the device is powered up, there will be a voltage range in which the device will not operate properly. The device should be reset once it has entered the normal operating range (from an out-of-voltage condition). The RESET pin may then be forced high. Other device operating parameters (such as frequency, temperature, etc.) must also be within their operating ranges when the device exits reset. Otherwise, the device may not function as desired. 2.3 Decoupling 2.2 Device Reset It is highly recommended that the MCP2122 have a decoupling capacitor (CBYP). A 0.01 µF capacitor is recommended as a starting value, but an evaluation of the best value for your circuit/layout should be performed. Place this decoupling capacitor (CBYP) as close to the MCP2122 as possible (see Figure 2-1). The MCP2122 is forced into the known state (RESET) when the RESET pin is in the low state. Once the RESET pin is brought to a high state, the device begins normal operation (if the device operating parameters are met). Table 2-1 shows the states of the output pins while the device is in reset (RESET = Low). Table 2-2 shows the state of the output pins once the device exits reset, RESET = L→H (device in Normal Operation mode). The MCP2122 has a RESET noise filter in the RESET input signal path. The filter will detect and ignore small pulses. Using the RESET pin to enter a low-power state is discussed in Section 2.9 “Minimizing Power”. FIGURE 2-1: VDD DEVICE DECOUPLING MCP2122 VDD VSS RESET 16XCLK TX RX CBYP (bypass capacitor) TXIR RXIR  2004 Microchip Technology Inc. Preliminary DS21894B-page 5 MCP2122 2.3.1 BROWN-OUTS FIGURE 2-4: VDD VDD R1 Q1 R2 40 kΩ RESET Some applications may subject the MCP2122 to a brown-out condition. Good design practice requires that when a system is in brown-out, the system should be in reset to ensure that the system is in a known state when the system exits the brown-out. This brown-out circuitry is external to the MCP2122. EXTERNAL BROWN-OUT PROTECTION CIRCUIT 2 2.3.1.1 External Brown-Out Reset Circuits Figure 2-2 shows a circuit for external brown-out protection using the TCM809 device. Figure 2-3 and Figure 2-4 illustrate two examples of external circuitry that may be implemented. Each option needs to be evaluated to determine if they satisfy the requirements of the application. MCP2122 Note 1: This circuit is less expensive, but less accurate. Transistor Q1 turns off when VDD is below a certain level such that: VDD • R1 R1 + R2 = 0.7V FIGURE 2-2: EXTERNAL BROWN-OUT PROTECTION USING THE TCM809 VDD VDD 2: Resistors should be adjusted for the characteristics of the transistor. TCM809 RST VSS RESET MCP2122 FIGURE 2-3: VDD EXTERNAL BROWN-OUT PROTECTION CIRCUIT 1 VDD 33 kΩ 10 kΩ 40 kΩ Q1 RESET MCP2122 Note 1: Resistors should be adjusted for the characteristics of the transistor. 2: This circuit will activate reset when VDD goes below (Vz + 0.7V), where Vz = Zener voltage. DS21894B-page 6 Preliminary  2004 Microchip Technology Inc. MCP2122 2.4 16XCLK (Bit Clock) The MCP2122 requires an external clock source to operate. The 16XCLK pin is the device clock input (see Figure 2-5) and is independent of the host UART interface or the IR interface. The 16XCLK determines all timing during device operation. It is the edge of the 16XCLK pin that causes activity to occur. The 16XCLK signal can also be referred to as a bit clock (BITCLK). There are 16 BITCLKs for each