Nuts and Volts - November 2009

DESIGNCYCLETHE

ADVANCED TECHNIQUES FOR DESIGN ENGINEERS

■ BY FRED EADY

TAKE AN IO-WARRIOR INTO YOUR

NEXT EMBEDDED BATTLE

We are all used to stuffing code into a microcontroller to enable our embedded applications. This month, the tables are turned. The microcontroller work has been done for us and we must perform some Bill Gates C++ coding to force bits back and forth across the USB pipe. The folks at Code Mercenaries have assembled a microcontroller package that embeds a fully compliant, low speed USB HID device. All we have to do to access the IO-Warrior’s I/O subsystem is plug the IO-Warrior into a USB port and perform the IO-Warrior API calls required to implement our application.

CODE MERCENARIES’ IO-WARRIOR

The IO-Warrior family (available through Saelig; see Resources) consists of the IO-Warrior 24, the IO-Warrior 40, the IO-Warrior 56, and the IO-Warrior 24 Power Vampire. The numbers in the IO-Warrior monikers represent the number of actual pins that make up the host microcontroller package. The 24-pin IO-Warrior 24 exposes 16 I/O pins to the programmer while the IO-Warrior 40 provides the programmer with 32 I/O pins. Fifty of the IO-Warrior 56’s pins are available to the user. The IO-Warrior 24 Power Vampire is a specialized variant that is designed to power source from the USB portal. All of the IO-Warriors are low speed USB devices with the exception of the IO-Warrior 56, which is a full speed device. The IO-Warrior 24 you see in Photo 1 is the one we’ll be working with. The IO-Warrior 24 is coded to include limited I2C master support, an HD44780 LCD driver, incoming RC5 IR command support, and SPI master mode support. There is also a special function mode that allows the IO-Warrior 24 to drive an 8 x 32 LED matrix with a little help from some external shift registers.

■ PHOTO 1. The IO-Warrior 24

comes as a kit.

The Design

Cycle version is shown here.

I added the solderless breadboard and the 2 x 16

Lumex LCD.

The basis of the IO-Warrior 24 is an OTP (One Time Programmable) Cypress CY7C63743C-PXC enCoRe USB combination low speed USB and PS/2 peripheral controller which you can see sans the IO-Warrior version label in Photo 2. The CY7C63743C-PXC’s claim to fame is its ability to automatically operate in USB or PS/2 mode with a minimum of external supporting components.

For you young’uns, a PS/2 is (was) an IBM personal computer that replaced the venerable IBM XT and AT personal computers. The PS is short for “Personal System.” USB overtook the clocked PC PS/2 interfaces in the 1990s.

To eliminate the more commonly used microcontroller support components, the CY7C63743C-PXC’s internal oscillator can be used in lieu of an external ceramic resonator, while a 3. 3 volt internal regulator provides voltage for the USB pull-up resistor. The CY7C63743C-PXC isn’t very good at sourcing current on its I/O pins ( 2 mA max). However, it makes up for the weakness by being able to sink up to 50 mA on a single GPIO pin. Otherwise, as you can see in Figure 1, the PXC is a typical USB-enabled microcontroller. A pinout diagram of it and