This document is the EVM user guide for the TCA8424. The device is a low-voltage keyboard scanner that
can support up to 128 keys, with open drain outputs that can sink up to 12 mA of current for LEDs. The
TCA8424 is fully HID over I2C™ compliant and is available with a pre-programmed keyboard map.
Contents
1About this Manual ........................................................................................................... 2
2Information about Cautions and Warnings .............................................................................. 2
This user’s guide describes the TCA8424 Evaluation Module (EVM). This guide contains the EVM
schematics, bill of materials, and top and bottom board layouts.
2Information about Cautions and Warnings
This section describes the jumpers and connectors on the EVM as well and how to properly connect, set
up, and use the TPS22985EVM.
This EVM contains components that can potentially be damaged by
electrostatic discharge. Always transport and store the EVM in its supplied ESD
bag, when not in use. Handle using an antistatic wristband. Operate on an
antistatic work surface. For more information on proper handling, see the
Electrostatic Discharge (ESD) application note (SSYA008).
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CAUTION
The information in a caution or a warning is provided for your protection. Please read each caution and
warning carefully.
3FCC Warning
This equipment is intended for use in a laboratory test environment only. It generates, uses, and can
radiate radio frequency energy and has not been tested for compliance with the limits of computing
devices pursuant to subpart J of part 15 of FCC rules, which are designed to provide reasonable
protection against radio frequency communications, in which case the user, at their own expense is
required to take whatever measures necessary to correct this interference.
The following items are required to program a TCA8424:
•TCA8424 EVM with un-programmed TCA8424 in socket
•Single 3.3-V supply
•MSP-EXP430G2 Rev 1.5 Launchpad with MSP430G2553 installed
•USB to mini-USB cable
•PC with Code Composer Studio installed running supplied firmware
•PC with Application GUI installed
The following items are required to evaluate at the system level:
•TCA8424 EVM with programmed TCA8424 in socket
•Breakout wires to connect to keyboard matrix rows and columns
•Keyboard matrix
•Host system with I2C plus INT connected to board
5Introduction
The benefits of the TCA8424 over other microcontroller-based solutions are lower development costs,
smaller package, and lower power consumption. The lower development costs are seen due to the
TCA8424 requiring programming of only 512 Bytes of OTP versus a full code stack on a microcontroller.
The TCA8424 is fully compliant with HID over I2C based systems with little to no host firmware
development.
The TCA8424 can also be used in a non-Hid over I2C environment by developing host drivers that mimic
the HID over I2C protocol to interpret the input reports. The EVM features a socket to allow easy
programming of multiple units for testing. The code stack supplied with the EVM is designed to interface
with the MSP430G2553 Launchpad to accomplish this. Once programmed, the EVM features breakout
headers for the keyboard and I2C connections to test in customer systems.
TCA8424 EVM Design Circuitry, Bill of Materials, and Connection Descriptions
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Table 1. Bill of Materials (continued)
295PANASONICERJ-3GSYJ122R16,R17, R18, R19, R20RESISTOR,SMT,0603,5%,1/10W,1.2K
300BOURNS3313J-1-204R14PlaceHolder, DO NOT INSTALL
320PANASONICECJ-1V41E105MC13PlaceHolder, DO NOT INSTALL
331Texas InstrumentsTCA8424RHARU1TIdevice to be used in Socket
345TE Connectivity382811-8N/AJumpers to be installed over P12, P13,
Pin 1 of J1 is a power input to the board and Pin 2 is the GND connection for the board. There are also 4
other GND test points in the corners of the board.
The TCA8424 cannot be powered from the MSP430 Launchpad when programming and needs
an external supply.
Figure 6. VCC and GND Connections
TCA8424 EVM Design Circuitry, Bill of Materials, and Connection Descriptions
6.5MSP430 Launchpad Interface
Headers P8 and P9 allow the EVM to interface with the MSP430 Launchpad. If not programming a unit,
jumpers P12, P13, P14, and P16 may be installed, header P15 should be removed. When programming a
unit, an external power supply is needed and all headers except P16 should be installed.
TCA8424 EVM Design Circuitry, Bill of Materials, and Connection Descriptions
6.6Breakout Pins
The breakout headers P1 and P2 allow connection of an external keyboard matrix to the EVM. P17 is
connected to the I2C lines of the TCA8424 allowing an external host to communicate to the TCA8424.
4. Connect the Launchpad to your computer with a USB to mini cable. A green LED and a red LED
5. Open Code Composer Studio and create a new workspace. Select the “Project” drop down menu and
6. After completing steps 1–5, to load the code at any point for any reason, simply open the workspace
If the Launchpad is running and VCC is not connected, the I2C communication will fail. You must
pause the debugger, reset the MSP430 with the "reset CPU" button and then press “play” again.
Launchpad Software Setup
should be on as shown below:
click on “Import existing CCS/CCE Eclipse Project.” Select Browse on the “Select-search directory”
option and select the location where the source code is stored. Click "Finish" and then select “debug
launch” to load the code to the MSP430G2553 microcontroller. Once completed, disconnect the USB
cable from the LaunchPad.
that was created. Ensure that the source code is the active project and the LaunchPad is connected
through USB. Then select “debug launch” to load the code.
5. Now the GUI has opened a connection to the Launchpad and the COM port remains in the drop down
GUI Walkthrough Guide
menu box as shown below:
After the connection the Launchpad has been established and the GUI can be fully utilized. The remaining
sections give basic steps on how to use each of the GUI buttons and inputs.
C. Changing the I2C Address
The I2C address in this GUI is referenced with the Read and Write bit included. An address of 0xA8 is
represented in binary as 1010100Xb with the last bit being a 'don’t care'. Address 0xA8 and 0xA9 are both
interpreted as the same address.
The GUI indicates whether an I2C Nack is received by the Launchpad, by presenting a dialog box like
shown below:
1. Both the Launchpad and GUI default the I2C addresses to 0x76 on startup as shown below:
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2. The I2C address must be written into the text box in the default format. Once an address has been
entered, simply click on the “Change I2C address” button to communicate this to the Launchpad.
•If the Launchpad is restarted, the I2C address will default again to 0x76 and must be changed
again if you are working with a different I2C address.
3. Since the default address of the TCA8424 is 0x76 when the OTP is not programmed, leave the default
address in the Launchpad.
1. The LED outputs can be changed using the HID Command “SET Report” in the GUI which replicates
GUI Walkthrough Guide
an HID host issuing the command. The LED values are off, by default, and are changed by clicking the
LED buttons.
2. The LED inputs for the SET Report command change to read ‘1’ with a green background when
clicked, and change back to ‘0’ with a red background when clicked again.
3. After inputting the LED values to be set, click the “SET Report button to set the output report and the
LED’s turn on.
4. Clicking the “Set Power Sleep” issues the SET POWER = WAKE HID Command and puts the device
to sleep. If the LED outputs are turned on when this command is issued, they will now turn off.
5. Issuing the SET POWER = WAKE command turns the LED’s back on after a Sleep command has
been issued. This is done by clicking the “Set Power Wake” command
6. The “Reset” button issues the RESET HID Command and the device resets, this clears the output
report. If LED’s were on previously, then they will turn off after this command is received.
7. The “Get Report” button issues the HID command GET REPORT. This retrieves the current contents
GUI Walkthrough Guide
of the input report and populates the text box below the button (red box). The GET REPORT
command does not clear an interrupt.
For more information on how HID commands operate and the TCA8424’s device behavior,
please see the “COMMAND and DATA REGISTER” section of the datasheet.
8. The “Read Report” button issues an unaddressed read command to the TCA8424. It populates the
same text box as the “Get Report” button does with the contents of the input report, but it will clear an
asserted interrupt.
For more information on the Input Report behavior please see the “INPUT REPORT” section of the
datasheet.
1. The first thing that must be created is the .csv file that contains the OTP contents. If this has been
created skip to step 2.
(a) Open an excel workbook with a single column for the OTP contents.
•The image below shows a properly formatted excel file with the blue box indicating a break in
the 512 byte contents:
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(b) Click the "Office" button and then click “Save as”.
(c) In the Save as window that pops up, choose the “CSV (Comma delimited) (*csv)” option under the
3. This opens a Windows®Explorer window that shows only .csv files. Navigate to the .csv file created
GUI Walkthrough Guide
earlier:
4. This populates the text box above the “Load OTP” button with the contents of the .csv file. This text
box is fully editable, as long as the contents remain in the same format.
5. Now choose a start location for our OTP programming and the number of bytes to program.
(a) The start location should be formatted as below and has no default contents. You must enter a
value before programming the OTP.
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(b) The number of bytes is defaulted to the value “512” and should be entered as a decimal value in
the text box, if it needs to be changed.
6. Now that the start location, number of bytes, and the OTP contents are in place, we are ready to
program the OTP. Upon completion, the following dialog box should appear:
7. The first byte of the OTP (Address 0x0000) contains the I2C address for the device including the R/W
bit. The R/W bit of the I2C address must be programmed to a ‘1’ for the OTP contents to be
used. If a ‘0’ is programmed at this bit, the OTP will program but the contents will not load into
the digital core.
8. Because we have now programmed a new I2C address into the device, we must change the I2C
GUI Walkthrough Guide
address in the Launchpad with the Change I2C address button.
•In this case it will now be 0x91 as shown below:
9. Now that the OTP contents are changed and the I2C address in the Launchpad is set, confirm that
what was actually programmed, matches what we tried to program.
(a) Click on the “Read OTP” button to read back the OTP contents in the device and populate the
textbox above the “Read OTP” button as shown below:
(b) Now compare the contents to be programmed with the current OTP contents by clicking the
“Compare OTP” button. If the "Contents to be Programmed" and the "Current OTP Contents" are
the same, the dialog below the “Compare OTP” button changes accordingly, as shown below:
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The Compare OTP button assumes the "Contents to be Programmed" and "Current OTP Contents"
are the same length. They must match exactly for dialog box to change to “Match”.
After Programming the OTP, the device will be in "TEST" mode until powered down and then
powered up again. This causes increased ICC outside of datasheet specifications. Once power
cycled, the device ICC returns to normal.
10Related Documentation
TCA8424 Low-Voltage 8x16 Keyboard Scanner with HID over I2C Compliant Interface Datasheet
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