Maxim Integrated MAXREFDES99 User manual

MAXREFDES99#: MAX7219 Display Driver Shield
Overview
Maxim’s MAXREFDES99# is an Arduino®form-factor shield which drives a 16x16
LED array for signage applications. This design is ideal for anyone developing a
display application. The board features Maxim’s MAX7219, a legendary LED driver
that simplifies the process of controlling multiple LEDs in matrix or numeric display
form. In MAXREFDES99#, four MAX7219 ICs are daisy chained to drive a full 256-
LED array, which can display any international alpha numeric symbol. The board
arrives complete with four 8x8 LED displays.
Code for the MAXREFDES99# is available on both Arduino and
ARM®mbed™platforms for quick prototyping with multiple platform boards. System
demonstrations include the display of ASCII characters ‘SPACE’ through ‘~’ and
writing/scrolling string messages. Developers are encouraged to build upon and
enhance the code base.
Features
•Flexible 16x16 Dot Matrix Display
•mbed.org library
•Arduino library
•Arduino form-factor shield
Competitive Advantages
•Portable
•Compact
•Flexible
•Cost Effective
Applications
•Displays
•Consumers
•Robotics

Introduction
LEDs, both low cost and available in many configurations, continue to dramatically
transform signage and lighting. The MAX7219 has long been the developer’s best
friend in LED driving, offering both simplicity and flexibility. Most systems, however,
drive 8x8 arrays, limiting the amount of communication, specifically character size,
and not utilizing the daisy chain feature of the MAX7219. 16x16 displays, in contrast,
provide the capability to display most international alpha-numeric characters.
Enter the MAXREFDES99#, which drives a 16x16 display, making it a powerful tool
for prototyping and developing applications.
The MAXREFDES99# is mbed and Arduino compatible, allowing fast development
for both platforms. The shield contains four daisy-chained MAX7219s that drive four
8x8 red LED dot-matrix displays installed on the top arranged to make a 16x16-
matrix display.

Figure 1. The MAXREFDES99# reference design block diagram.
Detailed Description of Hardware
See Figure 1 for a block diagram of MAXREFDES99#.
MAXREFDES99# can be powered from a wall-wart which provides a minimum of 7W
of power and an output voltage in the range of 7.5VDC to 12VDC. 7W is enough
power for the display, plus the microcontroller platform being used through the VIN
pin of the target platform. The reference design can be optionally powered from a
USB port while developing application code, however, the user must take care not to
exceed the power capabilities of the 5V rail supplied by their platform. The
recommended method of powering MAXREFDES99# is through a wall-wart
connected to J1.
MAXREFDES99# uses the MAX3390E level translator to provide a 3.3V logic-level
compatible interface to the four MAX7219 display drivers when using the shield with
3.3V platforms. The serial interface between the platform and the shield uses D10,
D11, and D13 for LOAD, DIN, and CLK respectively. The four MAX7219 display
drivers are daisy-chained connected with D11 connected to U3 and DOUT of U3
connected to DIN of U4 and so on. DOUT of U6 is left unconnected.

Detailed Description of Firmware
Libraries have been developed for both Arduino platforms and the online
development environment mbed.org which supports microcontrollers from several
manufacturers of ARM Cortex®-M microcontrollers. The source code for these
libraries and their corresponding 'Hello World' demo programs can be found in the
design files, or at the following links.
oArduino
oGitHub Link
ombed
oLibrary
oDemo Program
Figure 2 provides a high-level flow chart of the demo program for both platforms.
Figure 2. Demo program flowchart.

Quick Start
Required equipment:
•Windows®PC with a USB port
•MAXREFDES99#
•Compatible Arduino form-factor mbed platform
•7W min Wall-Wart with 7.5VDC to 12VDC output
Procedure
The reference design is fully assembled and tested. Follow the steps below to verify
board operation.
1. Connect MAXREFDES99# to your platform.
2. Connect wall-wart to J1 of MAXREFDES99#
3. Connect USB cable from the PC to your platform.
4. Follow the appropriate instructions below:
1. Arduino
1. Download the library from the GitHub repository
2. Follow the instructions herefor installing third party libraries.
3. Open your Arduino IDE, version 1.6.7 or later.
4. Navigate to File/Examples/MAX7219/MAXREFDES99_example
2. mbed
1. If you have never used mbed, setup an account and add your
platform to your online compiler per the instructions on your
platform's product page.
2. If you are using Windows and have never used serial
communications between your PC and your mbed platform,
follow the instructions here.
3. Navigate your browser to this link.
4. Click the 'Import this program' button and import the demo as a
'program'
5. Compile and download the resulting binary to your platform.
6. Open Hyperterminal, or your favorite terminal emulator, find the appropriate
COM port for your platform, and configure the connection for 9600bps, 8-N-1
with no flow control.
7. Ensure your terminal settings are configured for 'Auto' on Receive and
'CR+LF' on transmit.
8. Press the reset button on your platform and exercise the demo.
9. When running endless loops on the display, press the reset button on the
platform to stop the loop and return to the main menu.
`Data Available from: https://www.maximintegrated.com/en/design/reference-design-center/system-board/6251.html/tb_tab0