I/O Explorer™ USB Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
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There are three power options for servo connections: a common power bus (VU) for the I/O Explorer and servos;
separate on-board power busses for the I/O Explorer (VU) and the servos (VS); or an on-board power bus for the
I/O Explorer (VU) an external power bus for servos.
For the first case above: Install a shorting block on JP3 to connect the VS servo power bus to the VU power bus.
The servo power bus is then powered from the same source as the VU power bus. Powering a large number of
servos from USB power is not recommended. USB should only be used to power a couple of servos to avoid
exceeding the 500mA that a USB device is allowed to use.
For the second case above: Remove the shorting block from jumper JP3 to make the VS servo power bus
independent from the VU bus. In this case, the VS bus is powered from screw terminal connector J10.
Finally, for very high servo current applications, a separate power bus external to the I/O Explorer can be used to
provide servo power. In this case, remove the shorting block on JP1, tie the external servo power bus ground to
the I/O Explorer ground through the ground terminal on J10, and use pin 1 on the servo connectors to bring the
servo control signals out to the servos. The servo power and ground connections are made off-board.
The on-board servo power bus can be used to provide a maximum of 2A to each servo connector and 5A total to all
servo connectors.
9
Digilent Two Wire Serial Interface (DTWI)
The Digilent Two Wire Serial Interface (DTWI) provides a medium speed serial comunications interface compatible
with the Inter-Integrated Circuit (I2C
TM
) Interface defined by Philips. The I2C interface provides master and slave
operation using 7 bit device addressing. Each device is given a unique address, and the protocol provides the
ability to address packets to a specific device or to broadcast packets to all devices on the bus.
Access to the DTWI bus is provided using the DTWI API functions as described in the DTWI Programmer’s
Reference Manual in the Digilent Adept SDK.The DTWI connector, J12, provides two positions for connecting to the
I2C signals, power and ground. By using two-wire or four-wire MTE cables (available separately from Digilent) a
daisy chain of multiple I2C-compatible devices can be created.
The I2C bus is an open-collector bus. Devices on the bus actively drive the signals low. The high state on the I2C
signals is achieved by pull-up resistors when no device is driving the lines low. One device on the I2C bus must
provide the pull-up resistors. The I2C bus on the I/O Explorer provides selectable pull-up resistors that can be
enabled or disabled via jumper blocks JP4 and JP5. The pull-ups are enabled by installing shorting blocks and are
disabled by removing the shorting blocks. The shorting blocks are placed so that they line up with the SCL and SDA
labels on the board. Only one device on the bus should have the pull-ups enabled.
S
CL
S
DA
S
CL
S
DA
Pull-ups
Enabled
Pull-ups
Disabled
3
V
3
GND
3
V
3
GND
Jumper settings for I
2
C pull-up resistors.
