Digilent 410-221P User Manual

PPmmooddTTMMPP22™™ RReeffeerreennccee MMaannuuaal

Connector J1

–

I2C Communications

Pin Signal

Description

l

Revision: October 11, 2011

Overview

The PmodTMP2 is a temperature sensor and
thermostat control board built around the
Analog Devices ADT7420.

Features include:

• Up to 16-bit resolution

• Typical accuracy better than 0.25 °C

• I2C interface with 4 selectable

addresses

• 240ms continuous conversion time

• Support for 3.3v and 5v interfaces

• No calibration required

• Programmable

overtemperature/undertemperature
control pins.

Functional Description

The PmodTMP2 uses an 8-pin connector that
allows for communication via I2C, and provides
pins to daisy-chain the PmodTMP2 to other I2C
devices. The PmodTMP2 also provides two 2­pin headers for selecting the I2C address of the
chip, and two 2-pin headers for controlling
external devices based upon temperature
thresholds defined by the user in software.

I2C Interface

The PmodTMP2’s onboard ADT7420 chip acts
as a slave device using the industry standard
I2C communication scheme. To communicate
with the PmodTMP2 device the I2C master
device must specify a slave address (0x48­0x4B) and a flag indicating whether the
communication is a read (1) or a write (0). This
is followed by the actual data transfer. For the
ADT7420, the data transfer should consist of
the address of the desired device register
followed by the data to be written to the
specified register. To read from a register the
master must write the desired register address
to ADT7420, then send an I2C restart

1300 NE Henley Court, Suite 3

[phone] Voice | [phone] Fax

condition, and send a new read request to the
ADT7420. If the master does not generate a
restart condition prior to attempting the read,
then the value written to the address register
will be reset to 0x00.

As some registers stored 16-bit values as 8-bit
register pairs, the ADT7420 will automatically
increment the address register of the device
when accessing certain registers such as the
temperature registers and the threshold
registers. This allows for the master to use a
single read or write request to access both the
low and high bytes of these registers. A
complete listing of registers and their behavior
can be found in the ADT7420 datasheet
available on the Analog Devices web site.

Interface Connector Signal Description

1, 2 SCL I2C Clock
3, 4 SDA I2C Data
5, 6 GND Power Supply Ground
7, 8 VCC Power Supply (3.3V/5V)

The I2C interface standard uses two signal
lines. These are I2C data and I2C clock. These
signals map to the serial data (SDA) and serial
clock (SCL) respectively on the ADT7420.

Pullman, WA 99163

Doc: 502-221 page 1 of 2

Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners.

PmodTMP2 Reference Manual

Addresses

JP2 JP1 Address

I2C Address Selection

(MSB) of the temperature data, and the second
will be the least significant byte (LSB) of the
data. These two bytes form a two’s

Open Open 0x4B (0b1001011)
Open Shorted 0x4A (0b1001010)
Shorted Open 0x49 (0b1001001)
Shorted Shorted 0x48 (0b1001000)

The PmodTMP2 I2C bus can be set to use one
of four valid addresses. The top five bits of the
address are fixed, and the two least significant
bits are taken from the jumper states of JP2
and JP1. JP2 corresponds to bit one of the
address while JP1 corresponds to bit zero. An

complement 16-bit integer, if the result is
shifted to the right three bits and multiplied by

0.0625 the resulting signed floating point value
will be a temperature reading in degrees
Celsius.

For information on reading and writing to the
other registers of the device, as well as notes
on the accuracy of the temperature
measurements please refer to the ADT7420
datasheet.

open jumper corresponds to a one in the
address while a shorted jumper corresponds to
a zero. For example, when JP2 and JP1 are
open the device uses the address 0x4B
(0b1001011).

Open Drain Outputs

The PmodTMP2 provides two open drain
output headers for controlling external devices
based upon current temperature thresholds. If
the temperature leaves a range defined by
registers T

(0x06:0x07) and T

LOW

HIGH

(0x04:0x05) then the INT pin on J3 can be
driven low or high based upon the
configuration of the device. Similarly, the CT
pin on J2 can be driven low or high if the
temperature exceeds a critical threshold
defined in T

(0x08:0x09). Both of these pins

CRIT

are pulled up by 10KOhm resistors when they
are not driven by the device. For details on
their electrical specifications and configuration
of the INT and CT pins please refer to the
ADT7420 datasheet.

Quickstart Operation

When the PmodTMP2 is powered up, the
onboard ADT7420 is in a mode that can be
used as a simple temperature sensor without
any initial configuration. By default, the device
address register points to the temperature
MSB register, so a two byte read without
specifying a register will read the value of the
temperature register from the device. The first
byte read back will be the most significant byte

www.digilentinc.com page 2 of 2

Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners.