J2: I²C Daisy Chain Connector
• This is a 2×4 pin male connector that provides access to the I²C signals SDA and SCL as well as power from
the 3.3 V power bus and ground. This can be used to extend the I²C bus off of the board and to power
external I²C devices. Digilent has MTE cables and a selection of I²C peripheral modules that can be
accessed using this connector. All Digilent I2C Pmods are designed to be daisy chained if desired.
J4: Analog Signal Pass-Through Connector
• This connector passes the analog input pins on the host through the Pmod Shield board.
J5: Power Pass-Through Connector
• This connector passes the power connector from the host through the Pmod Shield board, and powers
the Pmod Shield from the host.
J6: Default SPI Connector
• This connector provides access to the SPI signals SS, MOSI, MISO, and SCK.
J7: I²C Connector
• This connector provides access to the same SCL and SDA pins provided on J2 but through a female header.
JA-JE: Digilent Pmod Connectors
• These connectors provide access to the signals of the host in a form factor which readily allows Digilent
Pmods to be connected. UART, SPI and GPIO protocols are supported via the Pmod connectors.
2 I
2
C Busses and Connectors
The Inter-Integrated Circuit (I²C) Interface provides a medium speed (100K or 400K bps) synchronous serial
communications bus. The I²C interface provides master and slave operation using either 7-bit or 10-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. Refer to the host board manufacturer's datasheet
for detailed information on configuring and using the I²C interface.
The Pmod Shield is designed to provide access to both I²C interfaces present on the Digilent microcontroller
boards. One of the I²C connectors is available on header J2 and the other connector is located on several other
connectors on the Pmod Shield. J2 is a standard 2×4 pin header connector with 0.100” spaced pins. It provides
access to the I²C signals, SCL and SDA, plus VCC3V3 and ground. The VCC3V3 can be used to power external I²C
devices. SCL and SDA are also provided on header J7 as female pins.
The I²C 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. Generally, only one set of pull-ups are used
on the bus. Jumpers JP10 and JP11 can be used to disable the on-board pull-ups on I²C #1 if a different value is
needed or some other device on the bus is providing the pull-ups or if I²C #1 isn’t being used and the pull-ups are
interfering with the use of the pins. The on-board pull-ups are enabled by install shorting blocks on JP10 and JP11.
Removing the shorting blocks disables the pull-ups.
