TB050 Monitoring Multiple Temperature Nodes Using TC74 Thermal Sensors and a PIC16C505 additional circuitry, although care should be taken to ensure that the combination of the PIC16C505 internal pull-up impedance with the cumulative load capacitance meets the timing requirements of the TC74. Proper delay times between clock and data transitions are provided by the application firmware.The PIC16C505 also has an internal oscillator and built in power-up circuitry eliminating the need for additional external components to provide these functions. Ward Brown Microchip Technology Inc. THEORY OF OPERATION The TC74 is a serially accessible digital temperature sensor that can determine temperatures in the range of 25°C to 85°C with ±2° absolute accuracy or 0°C to 125°C with ±3° absolute accuracy. Temperature information is retrieved from the TC74 via a two wire SMBus/I2C™ compatible interface. The TC74 represents the temperature as an 8-bit two’s complement signed integer that has a direct correspondence to the device’s temperature in degrees C resulting in a 1° temperature resolution. The TC74 is available in eight address versions so that eight devices can be monitored on the same two wire SMBus interface with no additional circuitry. This application uses a standard LCD module for temperature display. These modules are made by several manufacturers including Densitron, Epson, HewlettPackard, Optrex and Sharp. All of these manfacturer’s modules feature the same interface protocol. The display modules require an enable line, data latch, data direction, and 4 or 8 bits of parallel data. The number of data bits is software selectable during initialization. This particular application uses the 4-bit data option. Other applications may use other means of display or simply control several temperature control devices, such as fans. The PIC16C505 is a 14-pin MCU that can easily interface to the TC74. The PIC16C505 has built in pull-up resistors on several of the PORTB input pins. This feature permits interfacing to the mode control push buttons and the SMBus clock and data lines without any TC74A3 TC74A4 TC74A5 SCL 3 V DD 2 GND 5 SDA 4 3 V DD 2 GND 5 SDA 4 3 V DD 2 GND 5 SDA 4 3 VDD 2 GND 5 SDA 4 SCL +5V 10uF .01uF SCL TC74A2 SCL TC74A1 SCL TC74A0 3 VDD 2 GND 5 SDA 4 TC74 MULTIPLE TEMPERATURE MONITOR 3 VDD 2 GND 5 SDA 4 FIGURE 1: The TC74 is available in a 3.3 VDC configuration and the PIC16C505 operates with supply voltages as low as 3 VDC making low voltage applications possible. SCL Author: SOT-23A-5 +5V 1 Min. Max. 2 3 4 11 12 13 VDD RC5 RC4 RC3 RC2 RC1 RC0 RB5 RB4 RB3 RB2 RB1 RB0 VSS 14 PIC16C505 5 6 7 8 9 10 +5V 2 4 5 6 14 13 12 11 10 9 8 7 3 1 VCC RS RW E DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 VEE VSS 2X20 LCD Display 2001 Microchip Technology Inc. Preliminary DS91050A-page 1 Note the following details of the code protection feature on PICmicro ® MCUs. • • • • • • The PICmicro family meets the specifications contained in the Microchip Data Sheet. Microchip believes that its family of PICmicro microcontrollers is one of the most secure products of its kind on the market today, when used in the intended manner and under normal conditions. There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our knowledge, require using the PICmicro microcontroller in a manner outside the operating specifications contained in the data sheet. The person doing so may be engaged in theft of intellectual property. Microchip is willing to work with the customer who is concerned about the integrity of their code. Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not mean that we are guaranteeing the product as “unbreakable”. Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our product. If you have any further questions about this matter, please contact the local sales office nearest to you. Information contained in this publication regarding device applications and the like is intended through suggestion only and may be superseded by updates. It is your responsibility to ensure that your application meets with your specifications. No representation or warranty is given and no liability is assumed by Microchip Technology Incorporated with respect to the accuracy or use of such information, or infringement of patents or other intellectual property rights arising from such use or otherwise. Use of Microchip’s products as critical components in life support systems is not authorized except with express written approval by Microchip. No licenses are conveyed, implicitly or otherwise, under any intellectual property rights. Trademarks The Microchip name and logo, the Microchip logo, PIC, PICmicro, PICMASTER, PICSTART, PRO MATE, KEELOQ, SEEVAL, MPLAB and The Embedded Control Solutions Company are registered trademarks of Microchip Technology Incorporated in the U.S.A. and other countries. Total Endurance, ICSP, In-Circuit Serial Programming, FilterLab, MXDEV, microID, FlexROM, fuzzyLAB, MPASM, MPLINK, MPLIB, PICC, PICDEM, PICDEM.net, ICEPIC, Migratable Memory, FanSense, ECONOMONITOR, Select Mode, dsPIC, rfPIC and microPort are trademarks of Microchip Technology Incorporated in the U.S.A. Serialized Quick Term Programming (SQTP) is a service mark of Microchip Technology Incorporated in the U.S.A. All other trademarks mentioned herein are property of their respective companies. © 2001, Microchip Technology Incorporated, Printed in the U.S.A., All Rights Reserved. Printed on recycled paper. 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Le Colleoni 1 20041 Agrate Brianza Milan, Italy Tel: 39-039-65791-1 Fax: 39-039-6899883 United Kingdom Arizona Microchip Technology Ltd. 505 Eskdale Road Winnersh Triangle Wokingham Berkshire, England RG41 5TU Tel: 44 118 921 5869 Fax: 44-118 921-5820 08/01/01 DS91050A-page 3 Preliminary 2001 Microchip Technology Inc.