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U401 Connector Pin Out

Main Connector:

Along the long edge of the board is the SimmBus compatible connector, "J1". "J2" is immediately next to J1, and is connected one-to-one electrically.

Pin  Number SimmStick Signal SimmStick Signal Description U401 Signal
1 A1 Special IO <nc> (Pin 1 is located next to the silk screen "J1".)
2 A2 Special IO <nc>
3 A3 Special IO <nc>
4 PWR Unregulated DC
7.5 to 18V
5 A4 Special IO <nc>
6 A5 Special IO <nc>
7 +5V +5V +5V USB from PC
8 RES Reset (Active low) <nc>
9 GND Ground GND
10 SCL I2C Clock optional pull up
11 SDA I2C Data optional pull up
12 SI Serial In <nc>
13 SO Serial Out <nc>
14 A6 Special IO <nc>
15 D0 General Purpose IO PA.0 - Port A bit 0 (stepper motor control)
16 D1 General Purpose IO PA.1 - Port A bit 1 (stepper motor control)
17 D2 General Purpose IO PA.2 - Port A bit 2 (stepper motor control) (2-wire clock)
18 D3 General Purpose IO PA.3 - Port A bit 3 (stepper motor control) (2-wire data)
19 D4 General Purpose IO
(SS in slave mode)
PA.4 - Port A bit 4 (stepper motor control)
20 D5 General Purpose IO
PA.5 - Port A bit 5 (stepper motor control)
21 D6 General Purpose IO
PA.6 - Port A bit 6 (stepper motor control)
22 D7 General Purpose IO
PA.7 - Port A bit 7 (stepper motor control)
23 D8 General Purpose IO PB.0 - Port B bit 0
24 D9 General Purpose IO PB.1 - Port B bit 1
25 D10 General Purpose IO PB.2 - Port B bit 2
26 D11 General Purpose IO PB.3 - Port B bit 3
27 D12 General Purpose IO PB.4 - Port B bit 4
28 D13 General Purpose IO PB.5 - Port B bit 5
29 D14 General Purpose IO PB.6 - Port B bit 6
30 D15 General Purpose IO PB.7 - Port B bit 7


Other Connectors:

J3 is the USB connection. J4 and J5 are for factory use.

Power Connection:

The +5V available on pin 7 of the SimmBus is the power from the computer's USB port. Up to 100mA can be drawn from this supply to power devices attached to the U401. If more power is needed, an external supply should be used to power additional circuits. Do not attach the +5V from an external supply to this pin. The ground connection of the SimmBus should be common to any external power supply ground as well as any target circuits.

SimBus I2C Connection:

The pins labled "SCL" and "SDA" are the SimBus I2C connections. On the U401 the connections are not made to the microcontroller. There are two unpopulated PCB positions for pull-up resistors for these lines. The I2C communication interface relies on a passive pull-up and an active pull-down. The positions can be populated with resistors if no other pull-up resistors exist on the SimmBus I2C lines.

Board Layout:

Please see the FAQ for information about the components used in the picture.

Newest U401 (Rev 3) front view. This newest U401 has a lightweight  and removable USB cable.

Note that all lines extend from J1 to J2. There are then some J1 lines that only connect to J2, and no other circuitry.

Pin 1 on the U401 is located on the left, as you look at the board in the orientation above. Pin 30 is the pin on the far right.

Hardware:  U401 USB Interface    U421 USB Interface   U451 USB Interface

Programming:  USBm DLL Programming    Download Files

Application Notes:  U4x1 Application Notes    Misc Applications and Information    FAQ

While every effort has been made to make sure that the information posted on this site is correct, the author can not be held liable for any damages whatsoever for losses as a result of the application of this information. Use this information at your own risk.

USBmicro can design your custom and semi-custom USB product. Email about USB design can be directed to " Robert " at

Copyright © USBmicro, L.L.C., 2002-2010

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