1. Wireless Communications
SmartCar Project – Engineering Problem #7
Team: Alt_Facts
Team Leader:  Jared Long
Hardware Specialist:  Adam Musingo
Software Specialist: Brandon Lin
Team Assistant: Tyler Harclerode

2. Overview Problem Statement ……………………………………………………...(3)
Hardware ………………………………………………………………….(4)
Software …………………………………………………………………(10)
Summary…………………………………………………………………..(23)
Audience Questions ……………………………………………………….(25)

3. Problem Statement
How to implement wireless data link from car to monitoring PC (one way communication).

4. Hardware – Block Diagram
Digi Int. XBee S1 RF Module
Texas Instruments TXS0104E Voltage Level Translator

5. XBee RF Module By default, module operates in transparent mode.
This mode will be utilized for the Smart Car application.
Two modules act as a wired serial line replacement.
Hardware specifications
Supply Voltage : 2.8V- 3.4V 
USE 3.3V line!!!   DO NOT APPLY 5V!!! 
TX current : 45 mA
RX current : 50 mA
Idle current : 50 mA
Has an indoor range of 100'
Additional breakout board required for mounting (provided).
XBee RF module on 
Breakout board

6. XBee RF Module

7. TXS0104E Voltage Level Translator
Acts as the 'middle man' between MCU and XBee.
With 2 voltage levels applied, this unit will translate from one voltage level to the other and vice versa.
VCCA < VCCB
VCCA : wired to 3.3V
VCCB : wired to 5V
Constraints of the device
VCCA : 1.65V-3.6V
VCCB : 2.3V-5.5V
Max Date Rate : 24 Mbps (Push Pull) 2 Mbps (Open Drain)
OE (Output Enable) pin : wired to 3.3V.  This enables output.  

8. MCU Port Assignment
Must use the MCU's Serial Communications Interface (SCI) found at Port E.
E0 (TX) – Used to transmit serial data.
E1 (RX) - Used to receive serial data.
Wire the Port E pins to the 5V side of the Voltage Level Translator.
DO NOT wire Port E pins directly to XBee Module.  The 5 V output signals from TX will damage the XBee Module due to Electrical Over Stress (EOS).

9. Schematic: How to Wire Blue : 3.3V Red : 5V Black : Ground Green : TX
Purple : RX

10. A Successful Message Capture
Software Overview
The SCI Module
Software Implementation
Constants and Variables
Library Functions
Register Initializations for SCI Module
RTC Module Reprogramming
Helper Functions Assimilation
The Transmission Function
Transmission Verification
A Successful Message Capture

11. The SCI Module Provides Serial Communication Consists of 8 Registers
Wired/Wireless
Interface
Consists of 8 Registers
2 Baud Rate Registers (SCIxBDH, SCIxBDL)
3 Control Registers (SCIxC1, SCIxC2, SCIxC3)
2 Status Registers (SCIxS1, SCIxS2)
1 Data Register (SCIxD)
Features
Adjustable Baud Rate
Error Detection Using Parity Bits
8-Bit and 9-Bit Modes

12. Implementation - Constants and Variables
SCI Macro Definitions
Move “irdata” Declaration from “read_irarray()” to Global Scope

13. Implementation - Library Functions
string.h
void *memset(void *str, int c, size_t n)
Additional String Functions
char *strcat(char *dest, const char *src)
size_t strlen(const char *str)

14. Implementation – SCI Register Initializations
SCI Baud Register
𝐵𝑈𝑆𝐶𝐿𝐾 9600 𝐵𝑎𝑢𝑑 =
Write SCI1BDH, then SCI1BDL
SCI Control Register 1
Bit 4 = 9-bit mode
Parity
Bit 1 = Parity Enable
Bit 0 = Parity Type

15. Implementation – SCI Register Initializations (cont.)
SCI Control Register 2
Bit 3 = Transmit Enable
Bit 2 = Receive Enable
SCI Control Register 3
Bit 3 = Overrun Interrupt Enable
Bit 2 = Noise Error Interrupt Enable
Bit 1 = Framing Error Interrupt Enable
Bit 0 = Parity Error Interrupt Enable

16. Implementation - RTC Module Reprogramming
Message Generation Frequency
Approximately 4Hz
Different from Baud Rate
Timing Regulation
TPM Modules (Prescaler & Modulus)
Bus Clock - 16 MHz
TPM1 - 1 MHz Interrupts
TPM kHz Interrupts
RTC - 2 Hz Polling

17. Implementation - RTC Module Reprogramming (cont.)
RTC Can Be Modified!
To double the frequency, halve the period
Original 500 modulus becomes 250 modulus
Don’t forget to subtract 1!
Adjust All RTC-Dependent Functions
battery_compare() function
Other Functions?
Alternative Timing Methods

18. Implementation - Helper Functions Assimilation
Code is provided in note set #2

19. Implementation - The Transmission Function
Message Formatting
Ordered sequence of character bytes
Begins with “$SC”
Comma delimited
Message Terminator (\n)

20. Transmission Verification (PuTTY)
Plug base station into USB port of computer
Determine what COM port the computer assigned to the base station (MaxStream PKG-U)
Open Putty program (in ET apps folder)
Click serial radio button and enter COM? in Serial line text box
Click Open

21. Transmission Verification (PuTTY cont.)
This terminal will display what your base station is receiving
The terminal will be used to correct errors and verify correct transmission.
Shown is an example transmission from Smart Car 1

22. Transmission Verification (LabView)
LabVIEW provides a graphical user interface (GUI)
Open Console.vi provided by Prof. Sumey
Follow instructions shown in yellow box
Click the arrow in the upper left corner to run

23. Summary Start by wiring the X-Bee into the Smart Car
Plug the base station into the computer and determine COM port
Begin programming to send data via the X-Bee module in transparent mode
Verify correct formatting with PuTTY terminal
Run Console.vi to prove communications

24. References
MCF51JM128RM. Denver, Colorado: Freescale Semiconductor Literature Distribution Center, 1 June PDF.
Sumey, Jeff. “CET Microprocessor Engineering.” California University of Pennsylvania. Web. 18 Feb
TXS0104E. Dallas, Texas: Texas Instruments Incorporated, 1 May PDF.
XBee®/XBee-PRO® RF Modules. Minnetonka, MN: Digi International Inc, 23 Sept PDF.

25. Questions?