Jeremy Sandoval University of Washington May 14, 2013 Using UART Protocol to Communicate between the Digilent Atlys Board and PC Jeremy Sandoval University of Washington May 14, 2013

Overview Defining UART protocol UART purpose Getting started using UART How to test a UART Project Configuring the COM port Results Next Task

What is UART? Universal Asynchronous Receive/Transmit Universal means data format and transmission speeds are configurable Asynchronous means no clock line UART takes bytes of data from one end and transmits them in individual bits in sequential order. When data gets to destination, the bits are reassembled back into bytes. Advantage of UART: Less costly to utilize two wires to send information in serial format than multiple wires to send information in parallel format

UART Continued Method to communicate between the Spartan-6 Atlys Board and PC via a COM (serial) port The Atlys board contains an EXAR USB-UART Bridge The EXAR part XR21V1410 can deliver the data to the Spartan-6 using a two-wire serial port to pins A16 and B16 Source: http://www.digilentinc.com/Data/Products/ATLYS/Atlys_rm.pdf

Purpose What purpose could UART fulfil in the IBLROD project? Debugging When the General Purpose Input/Outputs (GPIOs), mainly the on-board LEDs, cannot be used to display an internal information Or need more detailed information to understand what a specific process is doing

Getting Started with UART Began by downloading a demo project from Digilent’s website Contained the ISE project that demonstrated the use of the General I/O and UART Operation shown in state diagram:

State Machine Explained

Testing the UART Demo Project In order to test the project need to: Upload .bit programming file to Atlys board Download EXAR USB-UART driver and install on the PC Install Tera Term, a terminal emulator program that will used as a serial communication port on the PC Switch USB cable from PROG port to UART port on Atlys board

Setting up the Serial Port In order for Tera Term program to properly read and display information, the connection settings must be set as specified in UART Demo top level module comments  Baud rate: data transmission speed bits/sec Data: 8 bit characters sent Parity:  Bit that acts as a check on a set of binary values (not used) Stop: One of a pattern of bits that indicate the end of a character

Results Pressing the left, right, up, or down button will display button pressed message Pressing center button will display welcome message LEDs connected with on-board switches at all times except when center button is being pressed For this operation, LEDs are tied to ground (won’t turn on with switch)

Next Task… Understanding ChipScope and Plan Ahead Xilinx tools that make it easier to debug and verify FPGA designs