Screw-terminals are not installed. The PCB is designed for 5mm screw-terminals, but 5.08mm should fit also.
The DB15 connector is not installed.
The USB connector is also not installed.
The 2x5 header JTAG is normally installed on the U3 and U3-OEM. This header is for factory use. You can use a mating header
for physical support purposes, but it should not connect to anything.
As an alternative to the screw-terminals and DB15, the U3 PCB has holes available for standard 0.1” pin-header installation.
Connectors J3 & J4 are 2x5 holes that provide pin-header access to the connections that would normally appear on the left and
right screw-terminals. The 2x8 connector J2 provides a pin-header alternative to the DB15 connector. All these connector holes
are always present, but J2 is obstructed when the DB15 is installed. The idea is that an OEM can connect ribbon cables to the pin-
headers, or even plug the U3 directly to the customers main board designed with mating pin-header receptacles. See Appendix B
for connector coordinates on the PCB.
J2
1
GND
2
VS
3
CIO0
4
CIO1
5
CIO2
6
CIO3
7
GND
8
EIO0
9
EIO1
10
EIO2
11
EIO3
12
EIO4
13
EIO5
14
EIO6
15
EIO7
16
GND
Table 2.12-1. J2 Connector Pin-Headers
J3
1
FIO4
2
FIO5
3
FIO6
4
FIO7
5
VS
6
GND
7
GND *
8
SPC **
9
VS
10
GND
* SDA on <1.30
** SCL on <1.30
Table 2.12-2. J3 Connector Pin-Headers
J4
1
FIO0
2
FIO1
3
FIO2
4
FIO3
5
VS
6
GND
7
DAC0
8
DAC1
9
VS
10
GND
Table 2.12-3. J4 Connector Pin-Headers
USB (USB1)
There are 4 holes for a standard Type-B USB connection (plus a couple large holes for mounting tabs). Looking at the bottom
(solder-side) of the PCB with the USB/LED end of the PCB up, GND (pin 4, black wire) is in the upper-right corner. Then
clockwise it goes Vbus (5 volts, lower-right, pin 1, red wire), D- (lower-left, pin 2, white wire), and D+ (upper-left, pin 3, green wire).
If you have a shield wire, it can be connected to either of the large mounting holes. If using a normal Type-B USB connector, it
must be installed on the component side of the PCB.
Alternative Power Supply
Generally 5 volt power is provided via the USB connector holes, and usually it is provided from the USB host. There are few
reasons, if any, to power the U3 from anything besides the USB host. The only valid reason we hear has to do with keeping the U3
powered even when the USB host loses power, which is an unusual requirement in itself since the U3 does not really do anything
without a USB host connected. If you are considering an external supply for reasons related to noise or stability, you are probably
"barking up the wrong tree" and should contact [email protected].
The power supply provided by USB is typically 5 volts +/-5% @500 mA. The basic way to use an alternate supply is connecting it
to hole 1 of the USB connector holes, instead of the supply from the USB host. Or if using a USB cable, cut the red wire inside the
cable and connect your positive supply lead to that (also might need a connection of the negative supply lead to the black wire but
don't cut it). You can also connect an external supply to VS/GND screw-terminals (after cutting the red wire in the USB cable), but it
is preferable to bring the supply in through the USB connector.
Note that USB ground and the external supply common/negative/ground must both connect to GND on the U3 (which could mean
just the ground in the USB cable is needed if the power supply is already connected to that same ground). Also note that you never
want 2 supplies connected directly to each other without any mechanism to prevent one supply from backfeeding the other.
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