EECS 373 Lab 6: Serial Bus Interfacing

Copyright © 2013  Matt Smith,

10/9/2014

Schedule

See posted lab schedule.

This is a two week lab and consists of two parts.

Part 1 is due within the first week and consists of the following.
1) Answers to questions and screen shots from the In-Lab assignment parts 1 - 3.
2) Answers to questions, screen shots and a demo for Post Lab Part 1.

Part 2 is due within the 2nd week and consists of the following.
1) Screen shots and a demo for Post Lab Part 2.

Overview

    A common way to connect microprocessor system components with the processor is with a serial bus. Typical examples of serial buses are the Universal Asynchronous Receiver/Transmitter (UART), Serial Peripheral Interface (SPI) and Inter-Integrated Circuit (I2C).  For this lab we will begin by observing example serial transmissions of each. We will then interface to a few representative components specifically a SPI digital to analog converter (DAC) and I2C combination analog to digital converter (DAC) and DAC. We will not interface to a UART device. While these are common and you will likely use one for your project, they are relatively easy to interface to.

Pre-Lab Assignment

    There is no Pre-Lab Assignment. You should review the Serial Bus Lecture slides and consider reading the basic overviews from such sources  as Wikipedia for UART, SPI and I2C.

In-Lab Assignment

In-Lab Part 1: Observing a UART Transmission

1.1) The Serial Hardware Components

You  will use the UART, SPI and I2C devices integrated into the SmartFusion Microprocessor Subsystem (MSS). There are 2 each in the subsystem. You have already used UART0 to provide the standard output for printf. UART1, SPI1 and I2C1 are conveniently ported to pins on the latest SmartFusion evaluation kit. See below on right side of kit: JP8 UART Header, JP9 I2C Header and J23 SPI Header.


1.2) Configure MSS Components and Program FPGA

Select UART_1, SPI_1 and I2C_1 with the MSS configurator. It is not necessary to have the other components selected.  

1.3) SoftConsole Project

If you open SoftConsole with Libero, a project will be created with the UART, SPI and I2C drivers provided in the directory. Be sure that SoftConsole  v3.3 is specified in the tool flow as we did in lab 5 before starting your Libero project. 

1.4) Simple UART Program Excercise

Write a simple UART program that will send the message "Go Blue". Everything you need is provided in the drivers directory. The header descriptions in the include files describe the function of the drivers. Explicit examples are provided. The drivers are in the "project name"_MSS_MSS_CM3_0_hw_platform project directory.

You will not be able to observe UART1 activity with a terminal emulator such as FUN terminal. Only UART0 is ported to the workstation (via USB to serial connection). Also, printf is associated with UART0 as the standard output so it will not work. You will have to use the serial output functions provided with the device drivers to output on the UART1 port and the Saleae to observe the transmission.

Set the UART up for the follwoing:
  1. 57600 baud
  2. 8 bit data
  3. no parity
  4. one stop bit
The following code snipet is a starting point.

#include <stdio.h>
#include <inttypes.h>
#include "drivers/mss_uart/mss_uart.h"

int main()
{
{
uint8_t tx_buff[10] = "Go Blue";
/* initialize the UART */

/* transmit the message Go Blue */

}
}

1.5) Observe UART Transmission with Saleae

Connect the Saleae (USB based Logic Analyzer from lab 1) to the JP8 header and observe the transmission. Enable the serial protocol analyzer, configure it to read the "Go Blue" message. Save a screen shot of the serial protocol analyzer showing the "Go Blue" in text display. Submit it with your post lab.


To observe the transmission with the Saleae, add an "Async Serial" analyzer to the wire connected to the tx channel. Make sure to configure it based on the values in the provided code. You can trigger the analzyer on the data line going low.



1.6) References

SmartFusion MicroController Subsystem Users Guide (UART Section)

Saleae Logic User Guide

The mss_uart.h. file in the device driver directory.

1.7) Post Lab Deliverables

Materials and Demonstrations
  1. Submit a screen shot of  the UART transaction using the asynchronous serial protocol analyzer showing the "Go Blue" message. 

In-Lab Part 2: Observing a SPI Transmission

2.1) Hardware

The hardware components and firmware (drivers) for the SPI devices were provided in the UART part 1 section.

2.2) Example SPI Program

The following C code sends the code  to the SPI serial port J23 SPI Header. Compile the code and observe it with the serial protocol analyzer in the Saleae. You should be able to see the information sent in the transmit frame as a HEX value. This code is taken directly from mss_spi.h.  Look in this file to get a full description of the functions.


#include <stdio.h>
#include <inttypes.h>
#include "drivers/mss_spi/mss_spi.h"

int main()
{

const uint8_t frame_size = 32;
const uint32_t master_tx_frame = 0x0100A0E1;

MSS_SPI_init( &g_mss_spi1 );
MSS_SPI_configure_master_mode
(
&g_mss_spi1,
MSS_SPI_SLAVE_0,
MSS_SPI_MODE1,
MSS_SPI_PCLK_DIV_256,
frame_size
);

MSS_SPI_set_slave_select( &g_mss_spi1, MSS_SPI_SLAVE_0 );
MSS_SPI_transfer_frame( &g_mss_spi1, master_tx_frame );
MSS_SPI_clear_slave_select( &g_mss_spi1, MSS_SPI_SLAVE_0 );
return(0);
}
}

2.3) Observe SPI Transmission with Saleae

Connect the Saleae to the JP8 header and observe the transmission. Enable the serial protocol analyzer, configure it to read the code message 0x01000A0E1 in HEX. Save a screen shot of the serial protocol analyzer with the transaction displayed in HEX.  Submit it with your post lab.

To observe, set a breakpoint on return(0) and set the logic analyzer to trigger on the select line going low.



2.4) References

SmartFusion MicroController Subsystem Users Guide (SPI Section)

Saleae Logic User Guide

The mss_spi.h. file in the device driver directory.

2.5) Post Lab Deliverables

Materials and Demonstrations
  1. Submit a screen shot of  the SPI transaction using the Saleae SPI serial protocol analyzer showing the message displayed in HEX format.

In-Lab Part 3: Observing an I2C Transmission

3.1) Hardware

The hardware components and firmware (drivers) for the I2C devices were provided in the UART part 1 section.

3.2) Example I2C Program

The following C code sends the code  to the I2C serial port JP9 I2C Header. Compile the code and observe it with the serial protocol analyzer in the Saleae.  Look in the mss_i2c.h file for an explanation of the functions.

#include <stdio.h>
#include <inttypes.h>
#include "drivers/mss_i2c/mss_i2c.h"

/*the target address is a 7 bit value! */
#define TARGET_ADDRESS 0b1111000

int main()
{
uint8_t transmit_buf[] = { 0x01, 0x02 };
uint8_t receive_buf[10];

MSS_I2C_init(&g_mss_i2c1 , TARGET_ADDRESS, MSS_I2C_PCLK_DIV_256 );

MSS_I2C_write
(
&g_mss_i2c1,
TARGET_ADDRESS,
transmit_buf,
sizeof(transmit_buf),
MSS_I2C_RELEASE_BUS
);

MSS_I2C_wait_complete(&g_mss_i2c1, MSS_I2C_NO_TIMEOUT);
return(0);

/* the following code is provided as an example I2C read */
/*
MSS_I2C_read
(
&g_mss_i2c1,
TARGET_ADDRESS,
receive_buf,
sizeof(receive_buf),
MSS_I2C_RELEASE_BUS
);
MSS_I2C_wait_complete(&g_mss_i2c1, MSS_I2C_NO_TIMEOUT); */


}

3.3) Observe I2C Transmission with Saleae

Connect the Saleae to the JP8 header and observe the transmission. Enable the serial protocol analyzer, set it up to read the transactions in HEX. Save a screen shot of the serial protocol analyzer for your post lab with the transaction displayed in HEX format. Notice that the transaction is not complete. Why ? Be prepared to answer this question for your post lab.



3.4) References

SmartFusion MicroController Subsystem Users Guide (I2C Section)

Saleae Logic User Guide

The mss_i2c.h. file in the device driver directory.

3.5) Post Lab Deliverables

Materials and Demonstrations
  1. Submit a screen shot of the I2C transaction.  The view should be using the Saleae I2C protocol analyzer.
Answer the following questions
  1. Why is the I2C transmission incomplete? That is, why can't you observe the transmission of 0x1 and 0x2?

Post-Lab Assignment

For the post lab assignment you will interface  two external devices to the SmartFusion kits: the SPI, DAC,  Microchip MCP4901 and the I2C, ADC/DAC, Philips PCF8951.  You will wire the devices to the kits with wire jumpers  and protoboard. Suggested layouts and connections will be provided. Finally, you will adapt the example code provided above to work with these devices. It will be necessary to read the data sheet and make some adjustments to the provided code. 

Post-Lab Part 1: Interfacing to the Microchip MCP4901 SPI DAC

1.1) The DAC

The Microchip MCP4901 is an 8 bit digital to analog converter (DAC) with a typical SPI interface. Keep in mind that  SPI interfaces can vary in number of connections, frame size (number of bits), bit ordering, clock phasing and max clock speed. This device is relatively typical and can be interfaced within the operational capability of the MSS SPI hardware.

1.2) The Data Sheet

Part of the work of being a microprocessor systems engineer is sorting through data sheets for relevant information. Much of this  data sheet describes and specifies the digital to analog behavior and quantifying this behavior. For the most part, you are just interested in sections that will allow you to connect  the DAC to the SmartFusion kit and configure the SPI interface.

Sections of interest in the data sheet are:
Section 1: Electrical Characteristics Figure 1-1 SPI Timing
Section 3: Pin Functions and Numbers.
Section 5: Serial Interface

SPI details  to consider:
  1. Frame Size
  2. Command and Data Sequence.
  3. Clock Phasing (determined by SPI transfer mode)
  4. Maximum Clock Rate
  5. Bit Ordering

1.3) Connecting the DAC to the SmartFusion Kit

You can use the pin function descriptions in Section 3 of the data sheet  to determine what each pin of the DAC should be connected to.  Here are the suggested connections.

Connections Between SmartFusion Kit and MCP4901.

Pin Function Description Connection
1 VDD Supply Voltage Use 3.3 volt supply from expansion board
2 CSS Chips Select (active low) Connect to SmartFusion SPI Select Control
3 SCK Serial Clock Connect to SmartFusion SPI serial clock
4 SCI Serial Data Input Connect to SmartFusion SPI output data
5 LDAC Sync Output Control (active low) Enable all the time by connecting to ground
6 Vref Reference Voltage for DAC Connect to VDD
7 VSS Ground Reference Connect to Expansion Board ground
8 output DAC Analog Output Put a 2 pin header on this connection to monitor with scope.

See the following wiring photos for suggested wiring.  For a quick review on prototyping circuits, see this link.  We will be using the SmartFusion expansion board to provide power connections. The board provides access to other IO (input/output) that will be used in the following labs and the projects.

1.4) Debugging and Verification

  1. Use the Saleae and protocol analyzer to verify your SPI settings with respect to the device specification.
  2. Use the scope or logic analyzer to make sure the correct signals and voltages are being applied to device.
  3. Check to see the analog output corresponds to the digital value applied.
  4. Start simple. Begin by just trying to produce a single analog voltage.

1.5) SPI Interfacing Post Lab Deliverables

Materials

Submit a screen shot of a SPI transaction showing a write of a mid value DAC value.  The view should be using the SPI protocol analyzer.
Demonstration

Write a software application that will produce a triangle wave at a frequency and Vpp (voltage peak to peak) of your choosing. Demonstarte to the  lab staff. 
Answer the following questions
  1. List the SPI configuration changes you had to make from the example code for the DAC interface.
  2. MSS_SPI_set_slave_select  sets the SPI select line. The evaluation kit provides just one select line on the SPI header. If we wanted to add another DAC, what is one way you could provide another select line? Consider that you can write your own  select function.
  3. What  SPI transfer mode (ie MSS_SPI_MODE1) did you have to use for the DAC and why (hint see figure 1-1 in the data sheet) ?

Post Lab Part 2: Interfacing to the Philips PCF8591 I2C ADC

2.1) The ADC

The Philips PCF8591 is an 8 bit digital to analog converter (DAC) and 8 bit analog to digital converter (ADC) with a I2C interface. Unlike SPI buses, the I2C is standard. The device control register and read/write sequences vary with each device.

For this part of the lab you will have to do all the work of sorting through the data sheet to interface to the device. No connection tables or photos showing connections will be provided. This of course is representative of actual engineering work and what we expect you to do for your project application. Essential suggestions and debugging hints are listed below.

2.2) The Data Sheet

For this device, you will sort through the data sheet to determine what you need to connect to the device and modify the I2C code.   As with the SPI data sheet, you will have to look for the relevant information. The I2C code provided is a starting point, but of course  you will have to make some changes and additions.  Use the same wiring approach used to wire the SPI DAC. You do not have to keep your SPI  hardware intact if you have demoed.

Software Considerations
  1. Take time to understand the I2C read and write protocol for this device. (page 14 of the data sheet)
  2. Take time to understand the meaning of the control register and meaning of each bit. (page 6 of the data sheet)
  3. Realize that the I2C address byte contain information besides the I2C slave address. (page 5 of the data sheet)
  4. See the details for using the MSS library I2C read and write functions in the associated include file.  (mss_spi.h)
  5. It is necessary to perform an I2C wait after an I2C read or write with the MSS_I2C_wait_complete.
  6. Take time to understand what initiates an analog to digital conversion and the association of the converted value to the conversion cycle . (page 9 of  the data sheet)
Hardware Considerations:
  1. Read the functional description of each pin and be sure you have it set or connected to the appropriate signal. (page 4 and 11 of the data sheet)
  2. The operational voltage range for the device is between 2.5 and 6 volts. The SmartFusion digital interface uses 3.3 volts so use 3.3 volts as the supply voltage.
  3. It is not necessary to pull up the I2C bus signals with pull up resistors.
  4. Program the analog inputs for single ended input.
  5. If you happen to reverse the supply voltage to the device, chances are it is damaged. Get another device from the instructor.
  6. The ADC and DAC need a clock to function. An internal clock is built into the device, but you have to enable it by attaching the EXT pin (12) to VSS (GND). DO NOT ground the adjacent clock pin. Leave it unconnected. 

2.3) Debugging and Verification

  1. Check that each pin of the device is connected correctly. Use a scope or logic analyzer to verify as necessary.
  2. Start by configuring the device to be an DAC. Write a single digital value that will produce an analog voltage. Measure the voltage to verify  it worked. Use the Saleae protocol analyzer to verify you are sending the correct sequence.
  3. Once you can do a DAC successfully, try a singe ADC cycle. You will require to I2C reads to do this. Why? (see software consideration 6). Use the I2C protocol analyzer to verify that you are sending the correct sequences and receiving the correct information.
  4. While your wiring does not need to be neat, excessively long wires can create transmission issues. Also use a bypass capacitor (>10uf) across the negavtive and positive supplies on the protoboard as shown in the wiring examples for the SPI DAC device.

2.4) I2C Interfacing Post Lab Deliverables

Materials and Demonstrations
  1. Submit a screen shot of a I2C transaction showing a DAC conversion of 0x1f.  The view should use the I2C protocol analyzer. Display values in HEX
  2. Submit a screen shot of a I2C transaction showing an ADC conversion of  the voltage generated by the DAC conversion of 0x1f (jumper the DAC output to the ADC input). The view should use the I2C protocol analyzer. Display values in HEX.
I2C Transaction Example

       See this image for an example transaction sequence. The sequence intializes the the device, writes the value 0xB3 to the DAC then reads from  analog channel 0.  The DAC output is connected to the ADC input. It is necessary to provide a delay between each write/read pair to allow for device latency.  The first value read from the ADC may not be the correct value.

Demonstration

Write a software application that reads DC values and displays them in terminal program scaled to volts. Demonstrate to a lab Instructor and get a signature using the Answer/Demo sheet.

Answer the following questions
  1. There are no post lab questions for this part.