EECS 373 Lab 6: Serial Bus Interfacing

Copyright © 2013  Matt Smith,

1/24/16

Schedule

Overview

Pre-Lab Assignment

In-Lab Assignment

In-Lab Part 1: Observing a UART Transmission

1.1) The Serial Hardware Components

1.2) Configure MSS Components and Program FPGA

1.3) SoftConsole Project

1.4) Simple UART Program Excercise

1. 57600 baud
2. 8 bit data
3. no parity
4. one stop bit

#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

1.6) References

1.7)  UART Screen Shot

In-Lab Part 2: Observing a SPI Transmission

2.2) Example SPI Program

#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

2.4) References

2.5) SPI Screen Shot

In-Lab Part 3: Observing an I2C Transmission

3.2) Example I2C Program

#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_960 );

	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

3.4) References

3.5) I2C Screen Shot

3.6) Questions

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

1.2) The Data Sheet

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

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

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

2.1) The ADC

2.2) The Data Sheet

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)

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