Designing a low cost CY7C63723 combination mouse(2)

The operation of the SIE is totally transparent tothe user. In the receive mode, USB packetdecode and data transfer to the endpoint FIFOare automatically done by the SIE. The SIE

then generates an interrupt request to invoke theservice routine after a packet is unpacked.In the transmit mode, data transfer from the

endpoint and the assembly of the USB packet arehandled automatically by the SIE.

also act as an input. The other two inputs thatare used for PS/2 communications are the D+/D-pins, normally used for the USB interface. Aconfiguration register also allows you to select anumber of configurations for these pins, meaningthat USB and PS/2 can co-exist on the samesignal pins.

Voltage Regulator

The CY7C63723 has a built in 3.3V regulator thatis designed to drive the USB D- pull up resistor.This regulator supplies a small amount of currentand should not be used as a general-purposeregulator. The output resistance of this regulatoris 200 , which necessitates a 1.3k resistor as apull up on the D- line to create the 1.5k resistorrequired by the USB specification.

The VREG pin is automatically turned off by theSIE (Serial Interface Engine) during USB datatransmission, so this pin should not be used as ageneral-purpose voltage reference.

When disabled, the VREG pin can act as an inputand is read via the port2 register.

General Purpose I/O

The CY7C63723 has 16 general purpose I/Olines divided into 2 ports: Port 0 and Port 1, aswell as four special input only pins.

A general purpose I/O pin can have two

selectable drive strengths: CMOS and resistive.CMOS mode is a general-purpose mode used fordriving logic and other relatively fast signaling.Resistive mode was designed to act as a pull upresistor with a value of about 14k , which in thisdesign will be used for pull up resistors on thebutton switches.

The CY7C63723 also has three sink modesincluding a super strong 50mA mode for driving,otherwise hard to drive, optics. It should be

noted that this microcontroller has a current sinklimit of 70mA total on all I/O pins at one time.In addition to these output modes, this

microcontroller has two user selectable inputthresholds for interfacing with TTL and CMOSlevel signaling.

Four additional inputs are available on the

CY7C63723. If the crystal-less oscillator is used,then the XTALIN pin can act as an input.

Hardware Implementation

The standard hardware to implement a mouse isshown in figure 1.0. For each axis (x & y for themouse ball, z for the wheel) there are a set ofoptics that output quadrature signals. For eachbutton there is a switch that is pulled up internallyby the built in pull up resistors. The D- line ispulled up via a 1.3k resistor connected to theVREG pin.

CY7C63723

Figure 1.0 Standard Mouse Hardware Connected to a CY7C63723

百度搜索“77cn”或“免费范文网”即可找到本站免费阅读全部范文。收藏本站方便下次阅读，免费范文网，提供经典小说教育文库Designing a low cost CY7C63723 combination mouse(2)在线全文阅读。