QUARC SPI Multiple I/O Expander Demo

This is an example of using multiple SPI devices with QUARC when those devices have support for hardware addressing. It is unusual in that it shows how to interface to multiple SPI devices when they have special support for sharing chip select lines. It interfaces with two MCP23S17 16-bit digital I/O expanders.

Warning

Note that SPI devices are not typically designed to share chip select lines. In general, each SPI device should have its own chip select line. The QUARC SPI Multiple Devices Demo shows how to interface to multiple SPI devices on the same SPI bus, where each device has its own chip select.

QUARC SPI Multiple I/O Expander Demo Simulink diagram

It is important to note that with SPI communications there are no signals to indicate whether a read or write is being performed. With SPI communications, data is always read and written at the same time. Hence, every write operation results in the same amount of data being read. Thus, when using the Stream blocks to communicate using SPI, it is important to always perform the write first followed by a read of exactly the same number of bytes. A Stream Write-Read block may be used for this purpose, or separate Stream Write blocks followed by a Stream Read block which reads the same number of bytes as the number of bytes written. The Stream Read will not cause another SPI bus cycle because the data being read will already be in the stream receive buffer.

System Requirements

This demonstration is run using the QUARC for Windows or QUARC for Win64 target with a Quanser QPID or QPIDe data acquisition card for SPI support. This example may also be run on other SPI-capable QUARC targets, such as the QUARC Linux DuoVero Target on the QBot 2 or QBall 2. No QPID(e) card is required in that case. Note that a software license for the desired target is required.

For a detailed discussion on the QUARC Linux DuoVero target and requirements needed to run models on this target, please refer to the QUARC Linux DuoVero Target reference page.

To run on other QUARC targets supporting SPI, the voltage levels will need to be checked (+3.3V required), and the port and frame option of the URI in the Stream Call block will likely need to be changed. Further details may be found below under the heading Running the example on a different target.

This example also requires two MCP23S17 16-bit digital I/O expanders from Microchip Technology Inc., wired to SPI port 1 of the target. The example requires the following connections to the MCP23S17 device, if a PDIP, SOIC or SSOP package is used. Do not use these pinouts for the QFN package! Refer to the datasheet for details.

Device Number	Pin	Name	Connection
1	9	V_DD	Wire to +3.3V.
1	10	V_SS	Wire to ground.
1	11	CS	Wire to SS of the QPID(e) to use as the SPI chip select.
1	12	SCK	Wire to SPI SCK of the QPID(e) to use as the SPI clock.
1	13	SI	Wire to SPI MOSI of the QPID(e).
1	14	SO	Wire to SPI MISO of the QPID(e).
1	15	A0	Wire to ground (bit 0 of hardware address).
1	16	A1	Wire to ground (bit 1 of hardware address).
1	17	A2	Wire to ground (bit 2 of hardware address).
1	18	RESET	Wire to +3.3V.
1	21	GPA0	Wire to pin 21 (GPA0) of device 2.
1	22	GPA1	Wire to pin 22 (GPA1) of device 2.
1	23	GPA2	Wire to pin 23 (GPA2) of device 2.
1	24	GPA3	Wire to pin 24 (GPA3) of device 2.
1	25	GPA4	Wire to pin 25 (GPA4) of device 2.
1	26	GPA5	Wire to pin 26 (GPA5) of device 2.
1	27	GPA6	Wire to pin 27 (GPA6) of device 2.
1	28	GPA7	Wire to pin 28 (GPA7) of device 2.

Device Number	Pin	Name	Connection
2	9	V_DD	Wire to +3.3V.
2	10	V_SS	Wire to ground.
2	11	CS	Wire to SS of the QPID(e) to use as the SPI chip select.
2	12	SCK	Wire to SPI SCK of the QPID(e) to use as the SPI clock.
2	13	SI	Wire to SPI MOSI of the QPID(e).
2	14	SO	Wire to SPI MISO of the QPID(e).
2	15	A0	Wire to +3.3V (bit 0 of hardware address).
2	16	A1	Wire to ground (bit 1 of hardware address).
2	17	A2	Wire to ground (bit 2 of hardware address).
2	18	RESET	Wire to +3.3V.
2	21	GPA0	Wire to pin 21 (GPA0) of device 1.
2	22	GPA1	Wire to pin 22 (GPA1) of device 1.
2	23	GPA2	Wire to pin 23 (GPA2) of device 1.
2	24	GPA3	Wire to pin 24 (GPA3) of device 1.
2	25	GPA4	Wire to pin 25 (GPA4) of device 1.
2	26	GPA5	Wire to pin 26 (GPA5) of device 1.
2	27	GPA6	Wire to pin 27 (GPA6) of device 1.
2	28	GPA7	Wire to pin 28 (GPA7) of device 1.

Warning

Note that the above tables only applies to the PDIP, SOIC and SSOP packages. Do not use these pinouts with the QFN package.

Wiring port A of the first digital I/O expander to port A of the second digital I/O expander is only to perform a digital loopback. This example writes a digital sine wave to port A of the second I/O expander and reads the values at port A of the first I/O expander.

Configuring the Demonstration

Open the QUARC Preferences dialog by selecting Preferences from the QUARC menu of one of the Simulink diagrams.

The URI used by the Stream Call block determines the baud rate and other options used for SPI communications. The options have been configured to match those required by the MCP23S17 devices and should not be changed. The baud rate, however, may be modified but should never be faster than 10 MHz (10e6) which is the limit for the MCP23S17 device.

To change the URI of the Stream Call block, double-click on the block to open its configuration dialog, as shown below.

Stream Call parameters

In the URI of host to which to connect field, replace the value of the baud option in the URI with the desired baud rate.

Click OK to close the configuration dialog.

Running the Model Using the QUARC Target for Windows

Please note that in order to be able to run this part of the demo, you must have purchased the QUARC Target for Windows as part of your license. In addition you must have satisfied the software and hardware requirements found in the QUARC Installation Guide.

To open the model click on the "Open this model" button found on the top right corner of this page.

Select External from the Simulation/Mode menu of the diagram, or select External from the simulation mode combo box on the toolbar.

Select Build from the QUARC menu of the diagram, or press Ctrl+B while the diagram is the active window. A great deal of output will appear in the Diagnostic Viewer about the progress of the build. If you cannot see the Diagnostic Viewer, you can open it by selecting View/Diagnostic Viewer from the menu of the diagram, or clicking on the View Diagnostics hyperlink at the bottom of the diagram. If you have MATLAB R2013b or earlier then the output will appear in the MATLAB Command Window.

If the build is successful, then the line:

*** Created executable quarc_spi_multiple_io_expander_demo.rt-win64

will appear in the Diagnostic Viewer. Finally, QUARC will download the model to the QUARC Target for Windows. The line:

### Model quarc_spi_multiple_io_expander_demo has been downloaded to target 'shmem://quarc-target:1' (54784 bytes)

will appear in the Diagnostic Viewer indicating that the code was successfully downloaded to the QUARC Target. If any errors occur, appropriate error messages will appear in the Diagnostic Viewer.

Double click on the Input and Output blocks to open the input and output Scopes.

Click on the Connect to Target button or select Connect to Target from the Simulation menu of the diagram to connect to the model.

Start the model by clicking on the Run button or selecting Run from the Simulation menu of the diagram. The Start item of the QUARC menu may also be used to both connect and start the model in one operation.

A sine wave will appear in the Input Scope as shown below. It shows the sine wave being written to port A of the second digital I/O expander. Notice that the Scope trace is moving in actual time. In other words, the trace passes the 10 second mark after 10 seconds have passed since in external mode, QUARC runs the model in real-time.

Input Scope

An identical sine wave should appear in the Output Scope as well, as illustrated below:

Output Scope

The identical sine wave appears because port A of the first I/O expander is wired to port A of the seecond I/O expander, so any value written to port A of the second I/O expander will appear at port A of the first I/O expander as the input value. Disconnecting one of the wires joining port A of the first I/O expander to port A of the second I/O expander will change the output of this Scope because one of the digital lines will no longer be looped back.

Click on the Stop button or select Stop from the Simulation menu of the diagram to stop the model. The Stop item of the QUARC menu may also be used.

Running the example on a different target

To run the example on a different target, refer to the instructions on the Running QUARC Examples on Remote Targets page.

The URI of the Stream Call block must be changed to suit the particular target. Below are sample URIs for different QUARC targets that support SPI:

Target	Port	Chip Select	URI
QUARC Windows Target with QPID(e)	0	SS	spi://localhost:0?word='8',baud='10e6',polarity='off',phase='off',frame='56'
QUARC Win64 Target with QPID(e)	0	SS	spi://localhost:0?word='8',baud='10e6',polarity='off',phase='off',frame='56'
QUARC Linux DuoVero Target on QBot 2	1	CS0	spi://localhost:1?word='8',baud='10e6',polarity='off',phase='off',frame='0'
QUARC Linux DuoVero Target on QBall 2	1	CS0	spi://localhost:1?word='8',baud='10e6',polarity='off',phase='off',frame='0'

When wiring the I/O expander on a different target, use the same wiring diagram but replace the QPIDe with the equivalent I/O on the target platform. The table above shows the SPI port and chip select to use for some sample targets.