Experiments with PIC16F628A

This project is the combination of the two experiments that we already did in past: Experiment No. 4 and 10. In experiment 4, we demonstrated how to use the mikroC 1-wire library to read temperature data from a digital sensor DS1820, and display the value on a LCD screen. Now we are going to use the hardware UART to transfer the temperature data from the PIC to a PC (Exp. No. 10). The Hyper-Terminal program running on a PC will receive the temperature values and display on screen. The temperature data from the microcontroller will be sent in every 15 sec. Experimental Setup: The setup for this experiment is same as the Experiment no. 10 with a DS1820 inserted in its 3-pin female header receiver on the board. The data output of DS1820 is connected to RB.0 (see articles  Exp. No. 4 and 1-Wire Protocol for detail). You need to rebuild the same TTL to RS232 level shifter circuit on a breadboard and set up a hyper-terminal to receive data at 9600 baud rate.

Introduction The DS18S20 is a 1-Wire digital thermometer device from MAXIM that provides 9-bit Celsius temperature measurements and communicates over a 1-Wire bus with a central microprocessor. It also has in-built alarm function with nonvolatile user-programmable upper and lower trigger points. The operating temperature range of the device is –55°C to +125°C with an accuracy of ±0.5°C over the range of –10°C to +85°C. Each DS18S20 has a unique 64-bit serial code, which allows multiple DS18S20s to function on the same 1-Wire bus. Thus, it is simple to use one microprocessor to control many DS18S20s distributed over a large area.

The 1-Wire is a registered trademark of Dallas Semiconductor Corp (now Maxim) for a serial communication protocol using a single data line and a ground reference. A 1-Wire Master (a microcontroller) initiates and controls the communication with one or more 1-Wire Slave devices (usually sensors). Each 1-Wire slave device has a unique, factory-programmed , 64-bit identifier, which serves as device address on the 1-Wire bus. This globally unique address is composed of eight bytes divided into three main sections. Starting with the LSB, the first byte stores the 8-bit family codes that identify the device type. The next six bytes store a customizable 48-bit individual address. The last byte, the most significant byte (MSB), contains a cyclic redundancy check (CRC) with a value based on the data contained in the first seven bytes. This allows the master to determine if an address was read without error. With a 248 serial number pool, conflicting or duplicate node addresses on the net are ne...

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