Digilent 410-174P - Manual (Page 6)

USB I/O Explorer Reference Manual
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The four analog output channels accessible
through DAIO port 2 are provided by a
Microchip MCP4728 serial D/A converter. This
port supports only single sample output mode.
The analog outputs for DAIO port 2 are
accessible via connectors JF and J1.
This analog output port supports two
selectable voltage references (2.048V and
3.3V).
UART Interface
The I/O Explorer provides a Universal
Asynchronous Receiver/Transmiter (UART)
interface for asynchronous serial
communications.
The I/O signals for the UART interface are
provided on Pmod connector JG. When using
the factory firmware, the UART interface is
accessed using the DACI API functions
provided in the Digilent Adept SDK and are
described in the DAIO Programmer’s
Reference Manual. The UART interface is
accessed as DACI port 0.
The signals provided at connector JG are logic
level signals. If RS232 signal levels are
required, a Digilent PmodRS232 can be
attached to connector JG to provide the level
translation and a DB9 connector for connection
to standard RS232 serial devices.
RC Servo Connectors
The I/O Explorer provides eight 3-pin RC
hobby servo connectors for direct control of
servos in embedded hardware actuator
applications. The servo connectors are
labeled S1-S8 and are accessible via the
Adept system DEMC servo interface. When
programmed directly, the servo connectors are
connected to the secondary microcontroller.
The servo connectors S1-S8 are accessible via
DEMC port 3.
In addition to the on-board servo connectors, a
second servo port, DEMC port 4, provides four
additional servo channels. This servo port can
be used with a Digilent servo connector
module, PmodCON3, connected to pins 7-12
of Pmod connector JE.
RC servos use a pulse width modulated signal,
PWM, to control the servo position. When
directly programming the secondary
microcontroller, the servo connectors on the
I/O Explorer board are intended to be driven
using timer interrupts rather than directly by the
pulse width modulators in the internal timers.
Digilent has a reference design available that
illustrates using timer interrupts to control
signal timing for the PWM signals to control RC
servos.
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.