With our last update, we looked at some of the features of the STM32F429ZTI chip on the STM32F429-DISCO board. Today, let's look at some of the features of the Discovery board on which the chip is mounted.
A dev board, of course, is more than just the processor on the board. A manufacturer will (hopefully) include a smattering of other devices on the board to help demonstrate the features of the microcontroller. In the case of the F429 Discovery board, the following features are included:
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STM32F429ZIT6 microcontroller featuring 2 Mbytes of Flash memory and 256 Kbytes of RAM in an LQFP144 package. (We discussed this in the last post.)
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An on-board ST-LINK/V2 on STM32F429I-DISCO (old order code) or ST-LINK/V2-B on STM32F429I-DISC1 (new order code). I have the older DISCO board and not the newer DISC1 board. To the best of my knowledge, the two will behave identically. Having an onboard debugger is handy: the debugger allows you to program the chip, and debug running code. As a bonus, the onboard debugger can be disconnected from the onboard STM32F429 chip and can be used to program any STM32 chip with just a few jumper wires.
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A 2.4" QVGA TFT LCD. The LCD driver is one of the features that really sets the STM32F429 apart from others in the crowded microcontroller market. While other chips are appearing that have an onboard LCD controller (such as the PIC32MZ-DA series), the price point and ready availability of the STM32 DISCOVERY boards (it seems like everyone has a discovery board from at least one of the STM32 series lying around) sets this board, and therefore this chip, apart from its competitors.
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64-Mbit SDRAM. While the primary use of this DRAM is to hold the framebuffer for the LCD display, the ability to store lots of data in RAM opens up interesting possibilities.
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An L3GD20 ST-MEMS motion sensor 3-axis digital output gyroscope. While not as versatile or ripe for playing as a 9 degree of freedom gyro/accelerometer/magnetometer, the gyroscope is nevertheless a fun part for demonstrating the capabilities of the MCU.
- Although the product sheet for the board touts six LEDs, let's be honest: there are two user-programmable LEDs on board. One is red and one is green.
- USB OTG connector. This is a nifty proposition. The STM32F429 can act as a USB device (say, a joystick, or a mouse, or a keyboard, or even, if we were to get really creative, it could be the brains of a printer or a scanner), or a USB host (that is, something that you can plug USB devices into). Theoretically, the onboard USB transceiver supports USB OTG functionality, which allows the chip to negotiate whether it's the host or the device. But frankly, I don't know enough about USB to dive into that, and I really don't care enough to learn. So USB OTG is not going to be part of this tutorial series.
- Expansion headers on 0.1" spacing that allow access to every pin on the STM32F429.
There are some features that have been left out of the Discovery board. For instance, there's no 32.768 kHz crystal to drive the real-time clock. Nor is there an Ethernet PHY and magjack. There are solder pads for a RTC crystal, though, so we might be able to remedy that issue by ourselves. I doubt that we'll be able to get Ethernet working.
While it's certainly not the biggest or baddest dev board on the market, the STM32F429-DISCOVERY has enough features included to make it a worthwhile learning and development platform. At a current price point of $30, it really has a high value proposition to hobbyists who'd like to step up from the Arduino ecosystem to something more capable.