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Microchip PIC Networks

Microchip PIC Networks. Amrit Bandy, Ben Funk Neil Goldsman. 2-Node Wired Set-up. PICs hooked up with wire connections PICs are small micro-controllers made by Microchip. Tx. Tx. μ P1. μ P2. Rx. Rx. µP: 16F88 by Microchip Features Built in A/D Conversion Module

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Microchip PIC Networks

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  1. Microchip PIC Networks Amrit Bandy, Ben Funk Neil Goldsman

  2. 2-Node Wired Set-up • PICs hooked up with wire connections • PICs are small micro-controllers made by Microchip Tx Tx μP1 μP2 Rx Rx • µP: 16F88 by Microchip • Features • Built in A/D Conversion Module • Universal Asynchronous Transmit and Receive using Tx and Rx ports. (Serial communication controlled by programmer)

  3. Step 1: Establish Network via Clock Synchronization • Node Clock Definition: • Built-in 8-bit timer, counts up from 0 to 255, sets off an interrupt upon overflow. Prescalar of up to 256 available. • Node Clock (our timer) updates every time the interrupt occurs (part of code) • Synchronization of Clocks • Node A transmits its NodeClock to Node B while Node B receives it and updates its own NodeClock

  4. Timer Synchronization Algorithm Node A: • Setup Tx Port for RS232 Transmission and Rx port for RS232 Reception using Universal Asynchronous Reception and Transmission • Check for hardware switch-If “on” goto 5 else 3 • Transmit packet comprising AB in hex (frame sync byte to intelligently qualify data packet to follow), followed by the NodeClock • Goto 2 (only one or two iterations needed) • Transmit NodeClock value to Real Terminal on Computer and print value on screen. Step 5 is to test the node synchronization

  5. Timer Synchronization Algorithm Node B: • Setup Tx Port for RS232 Transmission and Rx port for RS232 Reception using Universal Asynchronous Reception and Transmission • Check for hardware switch-If “on” goto 7 else 3 • Receive first byte, if it is not equal to ABh repeat 3. • Clear and start NodeClock • Receive second byte (clock of node A), add to NodeClock to update NodeClock • Goto 2 • Transmit NodeClock value to Real Terminal on Computer and print value on screen. Step 7 is to test the node synchronization

  6. Step 2: Data Transmission After Synchronization • Voltages represent sensor node reading • Each node compares its own voltage with voltage received from the other node and an LED is lit on the node with the highest voltage • Procedure: • Assign PIC_id for each node and COMM_id for the node that is transmitting • Establish Network by synchronizing clocks • Transmission and Reception are carried out in equal slots (TDMA) • Transmitting slot includes reading A/D data and transmitting packet • Reception slot includes receiving packet, comparing voltages of all the nodes, and lighting LED • Update COMM_id to give next node a chance to transmit data

  7. Data Transmission Algorithm • Synchronize timer to node A • If PIC_id=COMM_id goto 3 (transmit) else 7 (receive) • Read A/D voltage(10 significant bits) into two 8-bit registers, right justified • Transmit packet: ABh, NodeClock, highbyte(data), lowbyte(data) • Update COMM_id to allow next node to transmit • Wait for slot to expire, goto 2 • Receive first byte, if it is not equal to ABh goto 7. • Clear and start timer • Receive second byte, add to NodeClock to update NodeClock • Receive highbyte (data) followed by lowbyte (data), and store information for the node which is transmitting • Compare voltages for all nodes, light LED if self is highest • Update COMM_id, Wait for slot to expire, goto 2

  8. Step 3: Extend Wired Setup to 3 nodes • Issue: 16F88 has only one Rx port! • Solution: Use AND gate to choose correct line, since the transmitting line is high while receiving. Tx Rx Tx Rx Tx Rx µP1 µP2 µP3

  9. 3-Node Wired Setup Using AND Gates • Why AND gates? • Transmitting line is high while receiving • Truth Table shows that the AND gate reproduces the Tx signal

  10. Step 4: Remove the Wires – Employ Transceivers • Transceiver used: TR-916-SC-P by Linx Technologies • TXEN pin to enable Transmit • RXEN pin to enable Receive • Can only transmit or receive at a time • Algorithm remains the same except • Allow enough time for transceiver to start-up • Enable TXEN, disable RXEN for transmit • Enable RXEN, disable TXEN for receive

  11. Testing Steps 1-4 • Setup: 3 PIC 16F88 microcontrollers connected to potentiometers. Nodes B&C synchronize themselves to Node A, transmit their own voltages , receive that of the others, compare and indicate who is the highest using an LED. • Baud Rate: 19.2Kbps • Transmit/Receive Slots : 200ms with 20MHz clock • Results: Both the wired and the wireless models work for 3 nodes.

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