Production and testing
Software setup
Flashing
Functional test
Fault analysis
Component orientation
Voltages
Clock frequency

 Component orientation

There are several components whose footprint has a 180° or even 90° rotational symmetry, but the component's electrical function is not symmetric. Therefore, if such a component is incorrectly rotated, it will appear to the casual observer to be properly placed, but it will not work.

These components are:

atben components

atben only has the transceiver and the balun. The markings on both face towards the crystal and the antenna:

The corner next to pin 1 of the transceiver is marked with a small dot. The picture above also shows the orientation of the text printed on the package. The balun is marked with a square between pins 1 and 6.

atusb components

In atusb, the marking on the transceiver is on the corner between the crystal and the antenna. The marking on the balun faces towards the antenna. The microcontroller's "top" side faces towards the USB connector.

It is difficult to determine the LED's orientation by visual inspection. An efficient approach is to touch the LED's terminals with the probes of a multimeter set to measure resistance. The small current used for the measurement will light the LED.

 Supply voltages

The transceiver has three voltage domains:


On atusb, there is also the USB voltage domain at nominally 5.0 V.

Voltages should be tested in the following order: USB, then I/O, then digital, and finally analog. The table below gives the permissible ranges. Any voltages outside these ranges indicate a problem.

DomainNominalMinimumMaximum
USB5.0 V4.5 V5.25 V
I/O3.3 V3.0 V3.6 V
Digital1.8 V1.7 V1.9 V
Analog1.8 V1.7 V1.9 V

Measurement setup

The measurements should be performed with a digital multimeter. The transceiver's analog and digital supplies (1.8 V) are only activated when sending or receiving. To enable all voltage domains, put the transceiver in receive mode:

atrf-txrx
or
atrf-txrx -d net:ben
Exit with Ctrl-C.

To produce periodic transmissions in addition to enabling all voltage domains, use

atrf-txrx -p 3 -E 0
or
atrf-txrx -d net:ben -p 3 -E 0
Again, exit with Ctrl-C. Note that the transmissions may disturb nearby equipment operating in the 2.4 GHz band, such as 802.11 networks. This can be prevented by shorting the antenna to ground.

In case the board does not accept commands, only the USB and I/O voltage can be checked. If they are correct, proceed with checking the clock.

Measurement points on atben

The supply voltages on atben can be measured at the terminals of components as shown in this table:

DomainVoltageComponent
I/O3.3 VC3, C6
Digital1.8 VC5
Analog1.8 VC4

Ground can be accessed at the cover of the crystal. Note that the fiducials, while looking like test points, are not connected to anything.

This image shows the location of the measurement points:

Measurement points on atusb

The supply voltages on atusb can be measured at the terminals of components as shown in this table:

DomainVoltageComponent
USB5.0 VC1
I/O3.3 VC2, C10, C13
Digital1.8 VC12
Analog1.8 VC11

Ground can be accessed at the cover of the crystal, at the shield of the USB connector, or at the test point P11. Note that the fiducials are not connected to anything.

This image shows the location of the measurement points:

 Clock frequency

The precision of the crystal oscillator is crucial for operation. Anomalies are easy to detect with even a low-cost oscilloscope. This can pinpoint specific problems and help to select further analysis steps.

Oscillator tolerances

The crystal used in atben and atusb has a nominal tolerance of +/− 15 ppm at 22-28 C. Low-cost oscilloscopes typically have a timing accuracy of +/− 100 ppm, which means that only major excursions can be detected by measuring the clock output with such an instrument. Full-speed USB only requires an accuracy of +/− 2500 ppm. We can therefore consider all results within a range of +/− 1000 ppm as sufficient for an initial assessment, and perform more precise measurements by other means. This applies to atben as well as to atusb.

IEEE 802.15.4 requires the transceiver frequency to be accurate within +/− 40 ppm.

Measuring the clock on atben

atben normally does not output a clock signal. A 1 MHz clock can be enabled with the following command:

atrf-txrx -d net:ben -C 1
This configures atben as a promiscuous receiver. The reception of any IEEE 802.15.4 frame or pressing Ctrl-C will terminate the command.

The clock signal (CLKM) is available on the test pad shown on the image on the left, and it should look roughly as shown in the screen shot on the right:

 

ClockAction
0 HzCheck voltages; check that the clock is enabled; check for shorts around crystal; check connectivity of crystal
0.999-1.001 MHz, ~3.3 VppPerform precision measurement with atrf-xtal
OtherCheck voltages; check for contamination around crystal

Measuring the clock on atusb

The transceiver provides the clock for the microcontroller in atusb. A clock signal is therefore always available. Immediately after reset, the transceiver generates a 1 MHz clock. When the microcontroller comes out of reset, it raises the transceiver's clock output to 8 MHz and then enables USB.

The clock signal is available at the terminals of several components, either as the direct output from the transceiver (CLKM) or after passing a low-pass filter (CLK):

   

The left screen shot shows the clock (CLKM) before the low-pass filter while the right screen shows the clock (CLK) after the the low-pass filter.

ClockAction
0 HzCheck voltages; check for shorts around crystal; check connectivity of crystal
0.999-1.001 MHz, ~3.3 VppCheck presence of firmware; check for shorts on SPI signals; check connectivity of SPI signals
7.992-8.008 MHz, ~3.3 VppPerform precision measurement with atrf-xtal (@@@)
OtherCheck voltages; check for contamination around crystal

Note that, if testing a board into which no boot loader has been flashed yet, the clock frequency should be 1 MHz. If an unsuccessful attempt has been made to flash the boot loader, the frequency may be 1 MHz or 8 MHz, depending on how much code was successfully flashed.

Precision measurements (atben)

The clock frequency of atben can be measured with an accuracy of about +/− 100 ppm using the program atrf-xtal. atrf-xtal runs directly on the Ben and measures the duration of packet transmissions. The transmission time depends on the bit clock which is in turn derived from the oscillator.

ben# atrf-xtal 100
The number reported is the number of poll loops the CPU counted. This value should be compared to a reference count obtained with a known to be good atben board on the same Ben at a comparable temperature.

DifferenceAction
< +/− 50 ppmCorrect operation
< −80 ppmCheck soldering of capacitors; check for contamination around crystal
> +120 ppmidem
OtherDeviation can be compensated by adjusting trim value

Precision measurements (atusb)

The clock frequency of atusb can be measured with an accuracy of about +/− 1 ppm relative to the PC's NTP-disciplined clock.

pc# atrf-xtal 10000
This measurement runs for 10−60 seconds, depending on system load. Note that, in order to reach such a high precision, it is imperative that the PC clock be disciplined by NTP.

DifferenceAction
< +/− 30 ppmCorrect operation
OtherSee the atben section above

Production and testing
Software setup
Flashing
Functional test
Fault analysis

Last update: 2013-01-30  Werner Almesberger