DS41356B datasheet(32/54 Pages) MICROCHIP

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Low Pin Count USB Development Kit User’s Guide

DS41356B-page 28

2.7

PROJECT LAB 4 (CDC – SERIAL EMULATOR)

In this lab, the PIC18F14K50 is used as a serial emulator taking an RS-232 data trans-

mission using the Enhanced Universal Asynchronous Synchronous Receiver Transmit-

ter (EUSART) peripheral and converting it to the USB protocol within firmware. Many

embedded applications continue to use the RS-232 interface to communicate with

external systems. However, as USB becomes more prevalent, RS-232 ports are disap-

pearing from newer PC’s. A simple solution is to emulate RS-232 over the USB. In this

example, a virtual COM port is created that will allow the USB connection to appear as

an RS-232 COM connection. Furthermore, this example makes use of Windows drivers

that already exist eliminating the need to alter existing software such as the Hyper

Terminal application.

The RS-232 connector on the Low Pin Count USB Development Board is configured

so that the PIC18F14K50 can be used as a Data Terminal Equipment (DTE) device to

interface with Data Communications Equipment (DCE) devices such as alarm systems,

modems etc. To accommodate this lab and eliminate the need for the user to create

their own DCE interface circuitry, a Null-Modem Gender Changer has been provided in

the kit to crosslink the transmit and receive lines so that the Low Pin Count USB Devel-

opment Board can be converted from a DTE device to a DCE device. In this way, the

main concepts of serial emulation can be delivered using only two Hyperlink Terminals

on a single PC with one RS-232 serial COM port and one USB connection.

Microchip’s Full-Speed USB Firmware Framework provides information files (.inf) for all

of its CDC application examples that automate Windows driver alterations freeing the

user from doing this manually. Once the PIC18F14K50 has been programmed and

then connected to the PC USB port, Windows “New Hardware Found Wizard” will

prompt the user for additional driver information. At this point, the user need only direct

Windows to the directory containing the appropriate .inf file.

Microchip’s Full-Speed USB Firmware Framework provides all the source code

necessary to perform low-level RS-232 functions, thereby abstracting this from the

user.

NOTICE

Kits shipped with the RS-232 pin corrector (p/n 04-02087R1) do not require the Null Modem

Gender Changer but will instead require a female/female gender changer that does not cross-

link the transmit and receive lines. The pin corrector is not used in this lab as the RS-232 con-

nector on this version of the Low Pin Count USB Development Board is configured as a DCE

device. Applications using the Low Pin Count USB Development Board as a DTE device will

require the use of the pin corrector.

Note:

The only information that is required by the user in the .inf is the Vendor

Identification (VID) and Product Identification (PID) numbers specific to

their original design.

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