[SAM R21] SAM R21 Xplained Hardware Analysis (Part 4)

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[SAM R21] SAM R21 Xplained Hardware Analysis (Part 4) [Copy link]

Others We have analyzed the main hardware modules before, and now we are analyzing the remaining parts.

• Buttons and LEDs

The SAM R21 Xplained development board has a user button and a user LED. PA19 is connected to the LED through R303, and then connected to Vcc through the 330 ohm resistor R303; PA28 is connected to the button through R306 and R302. What are the functions of R301 and R306? Because PA19 and PA28 are also connected to the expansion port EXT1, R301 and R306 can be disconnected when necessary to prevent the LED and button from trying to conflict with EXT1. What is the function of the 39 ohm resistor R302? Why is this resistor connected in series with the button? It is because of the expansion port EXT1. If the EXT1 output is high and the button is pressed, R302 can protect the output signal on EXT1.

• I2C

There is not much to say about the onboard I2C. The standard usage is to pull up a 4.7K resistor to Vcc. When there are many chips connected to the I2C, this resistor can be appropriately reduced.

• Reset Circuit

EDBG or the reset button can reset SAM R21. The RESET signal of SAM R21 is pulled up to VCC by R300 by default, and C301 can prevent interference signals from affecting RESET. If EDBG is connected to the RESET of SAM R21 through R331, the reset button is connected to RESET through R304. These two 39 ohm resistors can play a protective role, the same as the role of R302 above.

• Power supply

The power supply of SAM R21 Xplained Pro is designed in a very standard way. Each VCC, VDDCORE, VDDIO, AVDD, and AVDOUT has a 100nF decoupling capacitor. VCC is connected to AVDD through the LC circuit of L300, C306, and C301 to prevent the digital noise on VCC from affecting the analog power supply.

• RF

The RF part is also the focus of the SAM R21 development board. Unfortunately, there are relatively few reference materials. Maybe ATMEL hopes that everyone will buy more modules. The development board has two antennas: the onboard ceramic antenna A600 and the external SAM antenna J600. J600 can be connected to a 2.4G whip antenna to enhance the RF signal. However, the onboard ceramic antenna is also very good and is generally sufficient. Unlike some development boards that use resistors to select antennas, the two antennas on SAM R21 are switched through the RF switch U600. U600 is AS222-92LF, its highest frequency is 3G, and its maximum loss is 0.5dB. U600 is controlled by POSWITCH_P and POSWITCH_N. B600 is a balun filter 2450BM15A0015E dedicated to AT86RF232 and AT86RF233. Its data sheet is at: http://www.mouser.com/ds/2/611/2450BM15A0015-242316.pdf.

• J304

J304 is connected to three IOs: PA09, PA12, and PA27. These are three pins that are not used elsewhere.

ljj3166

Really detailed.