chipKIT™ Basic I/O Shield™ Reference Manual
Copyright Digilent, Inc. All rights reserved.
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The FETs are labeled Q1A (pin 9), Q1B (pin 6), Q2A (pin 5), and Q2B (pin 3). These four pins are also four of the
pulse width modulation (PWM) outputs supported by the chipKIT boards. The FETs can be switched using PWM via
the analogWrite function.
An FET is switched on by driving its gate high. When the FET is on, it provides a low impedance path to ground
(similar to a closed switch to ground). When the FET is switched off by driving its gate low, it becomes a high
impedance path to ground (similar to an open switch to ground). Pull-down resistors are connected to the gate of
each FET to ensure that it is off unless being actively driven high by the microcontroller on the chipKIT board.
The FET outputs are accessed via screw terminal connectors J7 and J8 on the left side of the shield. The digital
signals used to switch the FETs on and off are also available on screw terminal connectors J9 and J10 at the left
side of the upper edge of the shield.
Screw terminal connector J6 is used to make the power and ground connections back to the external power
supply. The negative (-) pin of J6 connects the external supply ground with the Basic I/O Shield ground, and the
positive (+) terminal connects the Basic I/O Shield to the external supply voltage.
The unloaded 2-pin header JP1 can be used to connect the shield’s VCC5V0 power supply bus to the external
power supply bus so that the shield’s 5V supply can be used instead of an external supply. In this case, J6 is used to
connect the shield’s supply to the external loads. If this is done, the total current consumed by all external loads
must not exceed 2A or the current rating of the shield’s power supply (whichever is less).
2.4 I
2
C Bus
The I
2
C bus from the chipKIT microcontroller board is brought onto the Basic I/O Shield. There are two I
2
C devices
on the board and a connector for taking the I
2
C bus off the shield to connect to additional external I
2
C devices.
I
2
C Connector:
Connector J11 can be used to extend the I
2
C bus off of the shield to connect to additional external
I
2
C devices. J11 is a standard 2x4 pin header connector with 0.100” spaced pins. It provides access to the I
2
C
signals, SCL and SDA, plus VCC3V3 and ground. The VCC3V3 can be used to power external I
2
C devices.
The I
2
C bus uses open collector drivers to allow multiple devices to drive the bus signals. This means that pull-up
resistors must be provided to supply the logic high state for the signals. The Basic I/O Shield provides 2.2K-ohm
pull-up resistors. Generally, only one set of pull-up resistors is used on the bus. Jumpers JP2 and JP3 can be used to
disable the on-board pull-up resistors if a different value is needed or some other device on the bus is providing
the pull-ups. The on-board pull-up resistors are enabled by install shorting blocks on JP2 and JP3. Removing the
shorting blocks disables the pull-up resistors.
Digilent has several small I/O peripheral modules (Pmods) that can be connected using the I
2
C connector. These
include a 3-axis accelerometer, a 4-channel 12-bit A/D converter, a serial character LCD panel, a 3-axis gyroscope, a
real-time clock/calendar, and an I/O expander.
EEPROM:
A 256Kbit (32Kbyte), I
2
C EEPROM is provided using a Microchip 24LC256. This EEPROM, IC1, is located on
the bottom left of the shield, just below the chipKIT logo.
The 7-bit I
2
C device address for the EEPROM is ‘1010000’.
Digilent has a library for using the EEPROM. It is contained in document # DSD-0000311 (chipKIT IOShield
Library.zip) which can be downloaded from the Basic I/O Shield product page at www.digilentinc.com. The
EEPROM library is IOShieldEEPROM.
