Designing a low cost CY7C63723 combination mouse

with the Cypress Semiconductor CY7C63723 enCoRe USB

Microcontroller

Introduction

The Universal Serial Bus (USB) is an industrystandard serial interface between a computer andperipherals such as a mouse, joystick, keyboard,UPS, etc. This application note describes how acost-effective combination USB-PS/2 mouse canbe built using the Cypress Semiconductor

CY7C63723 USB microcontroller. The documentstarts with the basic operations of a computermouse peripheral followed by an introduction tothe CY7C63723 USB microcontroller. Aschematic of the CY7C63723 USB

microcontroller to the optics and buttons of astandard mouse can be found in the HardwareImplementation Section. The software section ofthis application note describes the architecture ofthe firmware required to implement the USB

and PS/2 mouse functions. This application noteassumes that the reader is familiar with theCY7C63723 USB microcontroller and the

Universal Serial Bus standard. The CY7C63723data sheet is available from the Cypress web siteat http://www.77cn.com.cn. USB documentation can befound at the USB Implementers Forum web siteat Available on-line from the USB ImplementersForum at IBM Personal System/2 MouseTechnical Reference

IBM Document #S68X-2229-00

IBM Personal System/2 Hardware InterfaceTechnical Reference - Common InterfacesIBM Document #S84F-9809-00

Introduction to the CY7C63723

The CY7C63723 is an 8-bit RISC microcontrollerwith an integrated USB Serial Interface Engine(SIE). The architecture executes general-purpose instructions that are optimized for USBapplications. The CY7C63723 has a built-in clockoscillator and timers as well as programmabledrive strength and pull-up resistors on each I/Oline. High performance, low-cost human-interfacetype computer peripherals can be implementedwith a minimum of external components andfirmware effort. For a detailed look at the

CY7C63723 please see the following document:

Mouse Basics

A standard PC mouse has a switch for eachbutton and a ball and rollers to measure

movement. The rollers are connected to opticsthat output quadrature information, which can bedeciphered into movement and direction

information. This application note shows how toconnect to and manage a standard configurationof mouse hardware, as well as handle the USBand PS/2 protocols. Each of these protocolsprovides a standard way of reporting mousemovement and button presses. For a betterunderstanding of these protocols you shouldhave four documents:

Universal Serial Bus Specification Revision1.1, September 23, 1998

Available on-line from the USB ImplementersForum at Device Class Definition for HID Version 1.1,April 7, 1999

CY7C63723/23 CY7C63742/43 enCoRe USB

Combination Low-Speed USB & PS/2Peripheral Controller

Available on-line from the Cypress

Semiconductor web at Clock Circuit

The CY7C63723 has a crystal-less oscillatorcircuit that eliminates the need for an externalresonator or crystal. This also frees up an

additional input on the XTALIN line. At power upthe oscillator will be within 5% of nominal 6MHz.Then as USB traffic starts up, the oscillator willself tune itself to within 1% of the 6MHz referencefrom low speed USB traffic. An external oscillatorcan be used by changing the value of the clockconfiguration register via firmware if your

application demands stand alone clock accuracy.

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