Texas Instruments SCAU020 Configuring the Board, Programming Configuration USB Cable Attached

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Configuring the Board

7Configuring the Board

The CDCE421EVM can be powered from the USB power supply or from an external source. The CDCE421EVM only needs a USB cable attached for programming purposes; however, for test measurements it is recommended to also use an external 3.3V power supply. Test measurements can also be taken with only the USB supplied power. Note that because of USB power variance, results may degrade. It is also possible to program the CDCE421 and then disconnect the USB cable with minor board configuration changes. To enable power and programming of any of the four blocks on the CDCE421EVM, the respective switch must be turned on as explained earlier.

7.1Programming and Testing Configuration (USB Cable Attached)—Default Configuration

By default, the CDCE421EVM is configured to operate with the USB cable attached and a 3.3V power supply added to AUX VDD and GND. In this configuration, the USB microcontroller is powered by the USB port 5V supply while the CDCE421 is powered by the 3.3V external supply. This setup is optimal for programming the CDCE421 device while also taking measurements. This configuration removes the power variations inherent with USB power supplies by isolating the CDCE421 from the USB supply.

7.2Programming Configuration (USB Cable Attached)

The CDCE421EVM can also use power supplied through the USB cable as its sole power source. However, because of power-supply variance in the USB supply, this configuration is not recommended for most measurements. Users are advised to enable this setup for saving configuration settings to the CDCE421 and later powering the device from its internal memory. (This option is useful if there is not a USB port available in a lab or test area.) In this configuration, JP1 must be moved from its default position to the new position shown in Figure 8. The Enable onboard power checkbox must be selected on the EVM software, followed by pushing the Apply button (see Figure 5).

Using￿external	Using￿only￿USB
3.3V￿supply	power￿supply

AUX

Figure 8. JP1 Setting for USB Programming Configuration

7.3Testing Configuration from a Saved Configuration (with USB Cable Removed After Programming)

When operating the CDCE421 without the USB programming cable (useful in lab settings where a PC is not immediately available at a lab station), the CDCE421EVM must be preprogrammed in one of the two configurations discussed above, and then reconfigured for external power supply usage.

Before making these board modifications, the CDCE421 settings must be saved with one of the two USB cable attached configurations. The Write Chronos Settings to EEPROM NO LOCKING software button must be used to save the CDCE421 settings to its internal EEPROM. After the settings are saved, the USB cable can be removed. Once the cable has been disconnected, JP1 should be in the Using External 3.3V Supply position (as shown in Figure 8). The EVM is now ready for use without the USB cable connected. The CDCE421 will always start from its saved configuration state in this mode.

If the CDCE421 must be isolated from the microcontroller, the switch corresponding to the block in use should be set to OFF for CE_x, SDATA_x, and LVPECL_TERM_x where x represents the block name (see Figure 9). The power line switch for the respective block, however, should remain on. This sequence also allows the user to remove the USB cable without affecting performance while the CDCE421 is powered on.

SCAU020 –March 2007 10.9MHz–1175MHz Low Phase Noise Clock Evaluation Board 13

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