TS-7970 Errata

Issue	Status	Description
RS232 prevents booting on REV A	Workarounds available, fixed in REV B	Early TS-7970 REV A boards may fail to boot if RS232 is connected before the board is powered. A small amount of RS232 idle negative voltage leaks from the transceiver to the FET controlling the switched 5V. The FET will not toggle while the output has a negative voltage, so the 5V rail never comes up. If this is a concern or if the issue is seen, we can rework the board to have a 2.5ohm resistor from SW_5V to 5V_A on U47 pins 4 and 5. REV A boards shipped after 01/13/2016 include this fix.
Boot is prevented if the USB Device port (not host) is plugged in without the console enable jumper.	Fixed in REV C	If the console jumper is not installed the silabs has USB VBUS, but no data signals. This puts the USB device into a locked up state while it waits to communicate on this bus. During this lockup it is unable to enable the signal that enables the rest of the rails to continue to boot the system. The fix is to disconnect VBUS from the silabs which is done on the REV C PCB. Temporarily, a cable without VCC can be made to work around the issue.