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Arduino + CPLD = CPLD Fun Board!

Homemade low cost CPLD dev board (Arduino STM32F103 and Altera MAX II EPM240/EPM570 CPLD). Two dev boards into one.

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Two dev boards into one: a STM32 based Arduino ("Maple Mini" compatible) and an Altera MAX II CPLD dev. board to start playing with VHDL/Verilog, or just to try to use a CPLD with the Quartus II schematic editor. The cost should be about 5/8$ plus the PCB (I haven't done the precise BOM calculation yet...), buying the components "around". The "pluggable" LCD module and the optional stand-alone 50MHz oscillator aren't included in the cost count.

The basic idea is to have a STM32 Arduino to use as "stimulus generator" for the CPLD (e.g. I2C master) and an Altera MAX II CPLD on the same board. In this way is easier to set up a complete "test bench" for the CPLD "application" (e.g. your custom I2C interface).


The CPLD Fun board in action:

The STM32F103 MCU is used as "stimulus generator" and as 8/36MHz clock generator for the CPLD, and is easily programmed using the friendly Arduino IDE through the USB connector.

Five push buttons (RST, BUT, USER1-USER3) and a led (PB1) are reserved to the MCU.

The STM32F103 MCU side is "Maple Mini" compatible, so it possible to use the STM32F103 Arduino core provided by http://www.stm32duino.com (more info here). For a short story about the Maple Mini and the stm32duino see here.

You need to flash the bootloader first using a cheap "St-Link V2" dongle through the SWD connector (or using a serial-USB adapter on the SERIAL connector. More info here).


To configure the CPLD (an EPM240T100C5 with 240 LEs, enough for some fun...) it is used the Quartus II IDE (free edition) and a cheap "USB Blaster" dongle through the JTAG connector.


A 4 digit 7-segment led display, four push buttons (USER4-USER7) and four leds (LED1-LED4) are reserved to the CPLD. There is also a connector for a common and cheap 1602A or 2014A LCD 5V module (that probably you already have got...).

On the CPLD side there are also a DEV_CLRn push button to clear all the internal FFs, and a DEV_OE jumper to force all the CPLD pins in HiZ (to use these two functions you must explicit enable them first in the Quartus II IDE).

An optional on-board 50MHz oscillator is available too (not assembled in the previous photos), and there are also two connectors for external oscillators.

There are 22 I/O lines that "join" the STM32 and the CPLD, and on every of them there is a pin of three connectors (TEST1, TEST2 and TEST3). In this way it is possible easily "observe" signals exchanged between them with a scope or a LA.

As far as I know, there is no commercial product that has this "feature".

On this 22 I/O lines there are available various peripherals (e.g. serial, I2C, SPI) on the MCU side.

There are also others 25 GPIOs on the CPLD side (GPIO1 and GPIO2 connectors).

It is possible to use the Arduino STM32 "side" or the CPLD "side" as a stand-alone dev board too, with the TEST1-TEST3 connectors acting as normal GPIOs (holding the pins of the other "side" in HiZ). This is an other unique "feature" of this board.

All this is shown in the following functional block diagram:


Typically, to program this board you need to use together the Arduino IDE for the MCU and the Quartus II IDE for the CPLD.

Here is a typical session (using the Quartus II schematic editor for the CPLD):

Of course you need two USB on you PC/Workstation, one to connect the Arduino IDE to the MCU USB (the STM32F103C8T6 MCU has an integrated USB peripheral) and one to connect the...

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A020216-R280617 BOM.ods

Components list (BOM).

spreadsheet - 6.62 kB - 03/03/2018 at 12:42

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S051117_MultiFun.ino

Arduino sketch for the "H051117_7MultiFun" CPLD configuration example.

ino - 10.80 kB - 11/07/2017 at 12:20

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S311017_7SegBCD.ino

Arduino sketch for the "H311017_7SegBCD" CPLD configuration example.

ino - 6.07 kB - 11/03/2017 at 09:31

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S161017_BlinkTest.ino

Arduino sketch for the "H161017_Blinks" CPLD configuration example.

ino - 2.52 kB - 10/28/2017 at 10:39

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Usb Blaster User Guide.pdf

Usb-Blaster User Guide (Altera/Intel).

Adobe Portable Document Format - 311.81 kB - 10/25/2017 at 14:27

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  • Tested the EPM570 PCB version!

    Just4Fun01/10/2018 at 16:02 0 comments

    At last I've assembled and tested the EPM570 PCB version:

    In the back of the PCB there is a short reminder about the solder jumpers you must use for the EPM570. In this case you need to populate C31 and C35 too (see the schematic).

    Of course in the Quartus II IDE you have to select an EPM570T100C5 as device too:


    As an example here is the file: H051117_MultiFun_EPM570.zip. It is the complete Quartus II project for the EPM570 version described in the log: Multi-functional display/leds/keys custom controller. Project example.

    The sketch for the STM32 is (of course) the same used for the EPM240 version.

  • Multi-functional display/leds/keys custom controller. Project example

    Just4Fun11/07/2017 at 07:29 0 comments

    This is a ready to use example of a custom "multi-functional" controller for a 4 digits 7-segments led display (single segment "graphic" drive mode with digits multiplexing), plus 4 status leds, plus 4 push buttons, using a bidirectional data bus (DATA_0-7) and a register selection bus (SEL_0-2). The command signals are an active low write signal (WR_EN) and an active low read signal (RD_EN). The behavior is very similar to a SRAM device.

    To make things easier, in this example it is used the schematic editor and the 7400 devices family library, but note that this is not the best way to use a CPLD (the right way is to use VHDL/Verilog languages...).

    The schematic is the following (it is better use the Quartus II schematic editor to view it, opening the project):

    The design is similar to the previous example. The input clock for the multiplex comes from the 36MHz clock (from the STM32 MCU), and is divided by two 1:256 dividers (74393).

    The internal digit registers are now 8 bits wide, because now each single segment can be controlled (plus the "dot"), and there is a 4 bits register for the four leds LED1-4.

    Only DATA_0-3 lines are really bidirectional, DATA_4-7 lines are not used in "read" mode and are tied to "1" using internal pull-up resistors.

    A logic "1" in the DATA bits means "led turned on" or "push button pressed".

    The "registers map" valid for the write operation is ("Reserved" means here "not used"):

    where the generic  "Digit n" byte used to turn on or off each single segment, is defined as:

      This one is for the read operation (to check the four USR4-7 buttons status):

    In the "read" mode there is no real register involved, so the SEL_0-2 lines are all "don't care".

    The complete Quartus II project can be downloaded from this file: H051117_MultiFun.zip (the file is too big for this site, so it's stored externally).

    Unzip it taking its directory structure, and open it from the main Quartus II menu with "File" -> "Open Project..." selecting the file .qpf:


    Upload the configuration into the CPLD as described in the Log: "Blink led example. Step by step guide".

    WARNING: Because this is a bidirectional interface, take in account the considerations done in the "The DEV_OE switch and led" Log. 

    The sketch for the MCU side is S051117_MultiFun.ino (in the "Files" section) and must be uploaded using the Arduino IDE to run an application example.

    The result is shown in this short video:

    The USR1-3 and BUT buttons are managed directly by the MCU.

  • Custom controller for a 7-segments display. Project example

    Just4Fun11/02/2017 at 22:05 0 comments

    This is a ready to use example of a custom controller for a 4 digits 7-segments BCD led display.

    To make things easier, in this example it is used the schematic editor and the 7400 devices family library, but note that this is not the best way to use a CPLD (the right way is to use VHDL/Verilog languages...).

    The custom controller has four registers (74175) to store the BCD digits, and drives a 4 digit BCD led display (already assembled on the board) with a BCD to 7-segments decoder (7449) using multiplexing. The input clock for the multiplex comes from the 36MHz clock (from the STM32 MCU), and is divided by two 1:256 dividers (74393).

    The interface for the MCU is so composed:

    • a 4 bits input data bus to receive a BCD digit (DATA_0-3);
    • a 2 bits input address bus to address one of four digit registers (SEL_0-1);
    • an input signal to write the digit to the selected digit register. The data and the address must be valid when the write signal is activated (SEL_WE).

    Here it is the schematic of the controller configured inside the CPLD:


    The complete Quartus II project can be downloaded from this file: H311017_7SegBCD.zip (the file is too big for this site, so it's stored externally).

    Unzip it taking its directory structure, and open it from the main Quartus II menu with "File" -> "Open Project..." selecting the file .qpf


    and double click on the file name to open the schematic editor:

    Here it is the schematic editor with the loaded project:

    Now upload the configuration into the CPLD as described in the Log: "Blink led example. Step by step guide".

    Then upload the sketch S311017_7SegBCD.ino (in the "Files" section) in the STM32 MCU using the Arduino IDE to run an application example using the custom interface.

    The result is shown in this short video:

    Note that pressing the DEV_CLRn button all the registers inside the CPLD are cleared.

  • The DEV_OE switch and led

    Just4Fun10/30/2017 at 17:59 0 comments

    As already said in the previous Logs, the DEV_OE switch forces all the CPLD I/O pins into a HiZ state. When the DEV_OE switch is in the HiZ position, the DEV_OE led is on.

    This switch comes handy in various way. A possible application is the case in which you want only use the STM32 "side" of the CPLD Fun Board, and use the TEST1-3 connectors as GPIOs pins of the MCU as a "Maple Mini" clone. In this way you can simply "freeze" the CPLD holding the configuration inside.

    But there is a situation in which this switch comes very very handy. Imagine that you are testing a custom interface loaded into the CPLD, and simulating this interface in a "real" situation using the STM32 as "stimulus" generator. Imagine that you have some output pins (signals from the CPLD to the STM32) and some input pins (signals from the STM32 to the CPLD).

    Now what it can happen if you want change, for any reason, an input as output and an output as input in the same change?

    Well, if you update the CPLD configuration at first, the new configuration will change an input as output, so this can generate a short circuit between the CPLD and the STM32 because there would be two output connected together.

    So you can decide to upload the new sketch at first with the new "scenario", but in this new sketch a STM32 pin will be changed as an output, so you have two output connected together too!

    The only way to break this "deadlock" is to use the DEV_OE switch to force all the CPLD I/O pins to an HiZ state and then upload the new CPLD configuration and the new sketch for the STM32 with the input/output accordingly updated. Only when both CPLD and the STM32 are updated you can safely revert the CPLD from HiZ with the  DEV_OE switch again.

    Remember that the DEV_OE needs to be explicitly configured in Quartus II IDE (the DEV_OE LED will turn on also if not configured!), as explained in the Log: How to configure Quartus II. Step by step guide,

  • Blink led example. Step by step guide

    Just4Fun10/24/2017 at 10:28 0 comments

    CPLD configuration design (Quartus II)

    Open yours previously saved project (see previous "Log") from Quartus II with "File" -> "Open Project..." and select the file "test1.qfp". The .qfp extension is used for the Quartus II projects:

    This is the environment:


    Now it is necessary to add a schematic sheet into the project.
    From the Quartus II menu click on "File" -> "New...":

    and select "Block Diagram/Schematic File". A new schematic file will be created:

    Now it's time to design the needed circuitry to blink a led inside the CPLD.

    In this basic example, to make things easier,  I'll use the schematic editor and the embedded library that emulate the well known 7400 device family to divide an input 36MHz clock till to about 2Hz. The 36MHz clock comes from the STM32 MCU using the STM32 MCO/PA8 pin (pin 29), that is connected to the CPLD GCLK1 (pin 14) pin . It will be possible see this signal using an oscilloscope connected to the pin 5 of J6 (TEST1 connector) and to the pin 8 of J7 for the GND (TEST2 connector).

    Of course to create the 36MHz output clock from the MCU, a sketch must be uploaded into the STM32 flash using the Arduino IDE. In the following we will examine this sketch too.

    Now I'll use three 74393 counters, each one connected to work as a 1:256 divider.

    Form the designer tool bar select the "Symbol Tool":


    and then type 74393 in the "Name" field:

    press the "OK" button and place three 74393 in the sheet (use the left mouse button to place):

    ... Read more »

  • How to configure Quartus II. Step by step guide

    Just4Fun10/23/2017 at 10:15 0 comments

    In the following I'll use Quartus II version 13.0SP1 (Service Pack 1) because for an other project I need the compatibility with the  Cyclone II FPGA series (this version is the must updated that supports those), and it is related to the EPM240T100 "flavor" of the CPLD Fun Board.

    After installing Quartus II IDE (you can get it from here after a registration) it is necessary change some default setting to better suit the CPLD Fun Board.

    This setting must be used for every new project, so in the following we'll see how to create a new project and apply the correct setting.

    From the Quartus II menu select "File" -> "New Project Wizard..."

    Click "Next >"

    Fill the directory for the new project, and the others names. I suggest to use the same name for all the fields (as done in the photo). Remember to avoid names with spaces inside! Then click "Next >" again

    click "Next >" again

    In the "Family" field select MAX II, in the "Package" field select "TQFP" and select in the field "Available devices" the row "EP240T100C5". Click "Next >" when done

    click "Next >" again

    click "Finish" . Now you have an empty template and it's possible change the setting.

    From the Quartus II menu select "Assignments" -> "Devices..."

    click on the "Device and Pin Options..." button

    set the "Enable device-wide reset (DEV_CLRn)" and "Enable device-wide output enable (DEV_OE)" check boxes. In this way you enable the "DEV_CLRn" key and the "DEV_OE" switch in the CPLD Fun Board.

    These are two important functions: the first will reset all the FFs inside all the LEs (Logic Elements) with the "DEV_CLRn" key, and the second will enable the possibility to set all the CPLD pins to HiZ using the "DEV_OE" switch.

    Some important notes about these two function:

    • The DEV_CLRn key is active also when all the CPLD pins are in HiZ;
    • When all the CPLD pins are in HiZ by means of the DEV_OE switch, the "DEV_OE" led is ON;
    • If you doesn't enable the "Enable device-wide reset (DEV_CLRn)" check box, the DEV_CLRn key will not operate;
    • If you doesn't enable the "Enable device-wide output enable (DEV_OE)" check box, the DEV_OE switch will not operate, but the DEV_OE led will turn ON anyway. This because it is not possible from the outside to know if this function is enabled or not.

    Now you will set up the state of all the unused CPLD pins. "Unused" here means not referenced explicitly in the "programming" phase.

    From the above windows, on the left side, choose "Unused Pins":

    and in the "Reserve all unused pins" field set "As input tri-stated weak pull-up". This is the best (and safer) option for the CPLD Fun Board.

    Now save this project. You'll use it later to set up a blink led example.

  • New PCB assembled and running

    Just4Fun10/19/2017 at 12:21 0 comments

    Here it is the new version:

    And a short demo video:

    Now it is possible use an EPM570T100 too, "configuring" the PCB with eight solder jumpers (see the legend on the bottom side of the PCB, or the schematic).

    The capacitors C31 and C35 are required only for the EPM570T100, so if you use an EPM240T100 do not populate them (as in the board shown in the photos, using an EPM240T100).

    Because currently I haven't any EPM570, when available I'll make an other board with it.

    In the files section I've added the schematic and PCB Gerber files (traces width/clearance is 7mil/7mil).

    There are also layout guides to help to assemble components for both the sides of the PCB, with both components reference  and value (file PCB_Layout_Guide.zip).

    The components list is here.

  • New PCB will support EMP240 and EMP570 CPLDs...

    Just4Fun09/14/2017 at 09:09 0 comments

    I've just finished the new PCB revision:


    With eight solder jumpers (SJ1-8) it is possible now "configure" the board to use an EPM240T100 or EPM570T100 CPLD (the idea to allow the choice between an EPM240 and an EPM570 was suggested by Hacker404).

    In the back side there is a short note on how use the solder jumpers.

    I've also added a switch and a led for the DEV_OE signal, because using the previous board version I realized that it would have been more handy.

    Now some more checks before send the files to the PCB service...

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Hacker404 wrote 09/14/2017 at 10:52 point

Looks good.

I feel a bit guilty now as I seem to remember some errata with a 5 Volt tolerant CPLD that I have used. I can't remember if it was with Xilinx XC9536XL / XC9572XL (QFP44) or Altera EPM240 / EPM570 (QFP100). I remember the data sheet had the pin functions on the left and the pin numbers for various packages on the right. It was a nightmare to read so it was not at all surprising that the document had errata.

So perhaps it might pay to check that your data sheet includes the errata correction before making the boards.

Love your work!

  Are you sure? yes | no

Hacker404 wrote 09/07/2017 at 09:07 point

This is looking good.

I guess you want five volt tollerant by your choice of the EPM240 as the cyclone II's are cheap now.

If you are redesigning the board you could also make it compatible with the EPM570 the has extra power/ground pins.

I usually run 5 Volt tollerant chips ate 3.6 Volts to improve noise margins.

  Are you sure? yes | no

Just4Fun wrote 09/07/2017 at 09:22 point

Thanks! The EPM570 costs too much compared with an about 1$ EPM240, so for that I think that it's better to switch to an entry level Cyclone II (probably next project...).

*UPDATE*

Just realized that an EPM570T100C5N can be found for about 3$ now... Hmmm...

  Are you sure? yes | no

Just4Fun wrote 09/14/2017 at 10:11 point

Said and done...! See the Log... :-)

  Are you sure? yes | no

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