Hardware Overview
As we mentioned in the Introduction, the Qwiic GPIO features the TCA9534 I/O Expander to communicate with up
to eight digital input/output pins via I C. In this section we'll examine the characteristics of the TCA9534 as well as
the features of the Qwiic GPIO breakout.
TCA9534 I/O Expander IC
The TCA9534 from Texas Instruments provides an I C to parallel digital input output interface. We'll cover the
basics here but for a thorough overview of the TCA9534 refer to the datasheet. The IC has an operating input
voltage range of
1.65V
to
5.5V
but we recommend powering it with
3.3V
via either the Qwiic connector or through
any of the
3.3V
and Ground pins to maintain compatibility with other Qwiic devices.
The TCA9534 supports both standard (100kHz) and fast mode (400kHz) I C frequencies. The IC also features an
active-low interrupt pin that is activated when any pins configured as an input have a different state from the Input
Port register state. This means you can connect this INT pin to an interrupt-capable pin on your microcontroller to
passively monitor devices connected to the TCA9534. For more information on this functionality, refer to section
8.3.2 in the TCA9534 datasheet and Example 4 - Interrupt in the Qwiic GPIO Arduino Library.
Three hardware pins (A0, A1 and A2) are dedicated I C address select pins. We've added three jumpers to the
Qwiic GPIO to allow users to have up to 8 boards on the same bus. The Solder Jumpers section below goes into
more detail on how those pins and jumpers are used on the Qwiic GPIO.
Latch Terminals
The Qwiic GPIO breaks out all eight of the TCA9534's I/O pins, the interrupt pin, as well as several power rail pins
(
3.3V
and Ground) to four 4-pin latch terminals so wiring peripherals to the board is extremely easy. All you need
to do is insert a stripped wire into your preferred terminal opening and press down firmly on the latch handle to
secure the wire into place.
What is an interrupt? In a nutshell, there is a method by
which a processor can execute its normal program
while continuously monitoring for some kind of event,
or interrupt. There are two types of interrupts: hardware
and software interrupts. For the purposes of this
tutorial, we will focus on hardware interrupts.
Handling PCB jumper pads and traces is an essential
skill. Learn how to cut a PCB trace, add a solder
jumper between pads to reroute connections, and
repair a trace with the green wire method if a trace is
damaged.
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