AN_106_Interfacing_USB_Printer_using_Vinculum_Host_Controller_FT_000064.pdf

Future Technology Devices International Ltd.

Application Note AN_106

Interfacing to a USB Printer using Vinculum

VNC1L Host Controller

Document Reference No.: FT_000064

Version 1.0

Issue Date: 2008-11-24

This application note describes how to add printing capability to an embedded design via a USB

interface using FTDIÓs Vinculum Host controller VNC1L. VNC1L implements USB Printer Class and

gives a command monitor port interface for controlling USB printers using standard PCL ASCII

commands. Details of how a battery operated portable printer HP-DeskJet 460 printer was

interfaced with FreescaleÓs 16-bit micro-controller HC12 using VNC1L on SPI monitor port are

presented.

This design can be applied to a variety of real-life embedded applications including medical

portable devices, field tester devices, logistics, point of sales, rentals, queuing systems, ticketing

system, gas receipts, etc. that require a printer interface. We highlight a product in the market

Quantifit from OHD that uses VNC1L to provide USB printer capability to a field fitness testing

device using the design in this application note.

Future Technology Devices International Limited

Unit 1, 2 Seaward Place, Centurion Business Park, Glasgow G41 1HH United Kingdom

Tel.: +44 (0) 141 429 2777 Fax: + 44 (0) 141 429 2758

E-Mail (Support): vinculum.support@ftdichip.com Web: http://www.ftdichip.com

Document Reference No.: FT_000064

Using Vinculum USB Host Controller Printer Interface Application Note AN_106

Version 1.0

Clearance No.: FTDI# 68

Table of Contents

1 Introduction............................................................................................ 2

2 Project framework ................................................................................. 3

2.1 Project Installation ..............................................................................................3

2.2 Project Structure .................................................................................................3

3 Software Theory and Command Structure .......................................... 4

3.1 Block Diagram: VNC1L Printer Interface Design ..............................................4

3.2 USB Printer Class Details ...................................................................................4

3.3 VNC1L Printer Interface Commands..................................................................5

3.4 Printer PCL Commands ......................................................................................7

3.5 HC12 Firmware Details........................................................................................8

3.5.1 Theory of Operation ................................................................................................................. 8

3.5.2 Firmware Routines................................................................................................................... 9

4 Hardware Connections and Running the Demo ................................ 10

4.1 Jumper Settings ................................................................................................10

4.2 LED Usage..........................................................................................................12

4.3 Printer Output ....................................................................................................12

5 Summary .............................................................................................. 13

6 Contact Information............................................................................. 14

Appendix A Î Acknowledgements ........................................................... 15

Appendix B - References .......................................................................... 16

Appendix C Î HC12 Firmware Source Code ............................................ 17

Appendix D Î Revision History................................................................. 25

Document Reference No.: FT_000064

Using Vinculum USB Host Controller Printer Interface Application Note AN_106

Version 1.0

Clearance No.: FTDI# 68

1 Introduction

In the printer marketplace, USB is the defacto interconnect standard for personal printers. The Universal

Serial Bus (USB) has several advantages over previous generation of connection methods such as parallel

ports. A USB port is much faster than a parallel port (can handle 12Mbps) and a single port can handle

different devices e.g. a USB port can handle USB Flash disks, mouse and keyboard whereas the parallel

port was dedicated for the printer connection. The USB enumeration process that occurs when a device is

connected to the USB host handles the device requirements using standard USB descriptors supplied by

the device. This is completely transparent to user. Users just plug in the printer and see it is ready for

use.

USB 2.0 specification defines a specific device class for printing devices. VNC1L USB Host controller

implements and supports USB print class device, configuration, and interface and endpoint descriptors as

per USB printer device specification. It also supports USB printer class specific request and response

structure used by basic Printer Command language (PCL) interface. Note: The VNC1L Host does not

provide drivers for printers.

Most modern printers support built-in fonts and as such they can print text, using basic printer control

codes, directly from the Vinculum Monitor. Other printers will require embedded fonts or graphics to be

sent as part of a print job. Most modern printers support a PCL language as the protocol for an operating

system driver to communicate with the printer. If the printer supports PCL language it can be controlled

by the VNC1L using the methods outlined in this application note.

Document Reference No.: FT_000064

Using Vinculum USB Host Controller Printer Interface Application Note AN_106

Version 1.0

Clearance No.: FTDI# 68

2 Project framework

2.1 Project Installation

The VPD.msi is the installation file for the project. When this file is run, the installer will install the project

files into C:\Program Files\Vinculum Printer Demo folder (the installer will give an option for selecting the

target folder). After successful installation the target folder is created and all source code files will be

present as per the file structure shown in Figure 1 below.

2.2 Project Structure

Project Folder: ÐC:\Program Files\Vinculum Printer DemoÑ contains a project repository of all the files

needed to implement the project. These include source code, PCB GerberÓs, output files, readme files and

tools used for implementing the demo. The structure of the project folder is shown in Figure 1.

Figure 1 Directory Structure

Output: This folder contains following files

Vdem7.sx

Distributable source code. It can be used to flash into microcontroller but doesnÓt

contain source listing when loaded into debugger.

Vdem7.mrk

Assembler output file, used for debugging.

Vdem7.bbt

Assembler Output file, probably used for debugging.

Vdem7.dbg

Debugger File

Vdem7.abs

File to be loaded into debugger (hiwave.exe)

PCB: This folder contains all the Gerber, Solder Mask, Silk Screen and Drill files for designing the Printer

daughter board.

Readmes: This folder contains readme files with more details on firmware files, version etc.

Source: This folder contains the assembly source code and list files for memory maps

Vdem7.asm

Assembly source code (text file)

Vdem7.lst Listing file, provides memory locations for program code (text file).

Tools: For developing this demo application we have used the FTDI V-Eval utility V-Eval.exe. This

provides the user with a terminal application that acts as a debug tool to intercept the messages on the

VNC1L monitor port. This application is provided in the tools folder, along with the links to the IDE used

for writing the Freescale assembly code.

Document Reference No.: FT_000064

Using Vinculum USB Host Controller Printer Interface Application Note AN_106

Version 1.0

Clearance No.: FTDI# 68

3 Software Theory and Command Structure

3.1 Block Diagram: VNC1L Printer Interface Design

SW1

USB-2

Freescale

HC12

Micro-

controller

SPI

Vinculum VNC1L

USB-1

HP DeskJet 460

Daughter

board

V-Eval Board

Figure 2 Block Diagram of VNC1L USB Printer Interface

Figure 2 shows the connections between the various devices used in this application note. An FTDI V-

Eval board is used as the base development platform. This includes the VNC1L device, prototyping area,

external connectors and two USB Host ports. An external microcontroller is required to control the

VNC1L. In this application note, a Freescale micro-controller on a daughter board is connected to the V-

Eval on the SPI bus.

The VNC1L monitor port is selected on V-Eval board through jumper settings (see Section 4.1). Three

interface options are possible Î UART, SPI and FIFO. In this set-up the monitor port SPI interface was

used. The Freescale micro-controller is then connected to the V-Eval SPI header.

When a printer is attached to Type A USB port of the V-Eval board, it is enumerated and a status

message is sent to the monitor port. This status message is captured by the HC12 micro-controller. The

VNC1L has two modes of commands - text based command and binary commands. To reduce the

bandwidth on the SPI bus, the binary command set (also called the Short Command Set) is used.

In the micro-controller unit firmware, pressing switch SW1 on the V-Eval board generates a set of PCL

commands which are sent to the VNC1L on the V-Eval board via the SPI interface. VNC1L sends the

corresponding data on the USB to the printer. The printer takes the data, parses it using PCL and prints

the data to the paper. LED7 and LED8 on V-Eval board are used to indicate the status of printer (see

details in Section 4.2).

The same concept can be implemented in Windows Mobile devices (based on Win CE) that interface with

Vinculum VNC1L chip on monitor port. Applications can be written to send PCL commands to the printer.

3.2 USB Printer Class Details

USB Printer Class specification defines three class-specific requests Î GET_DEVICE_ID,

GET_PORT_STATUS and SOFT_RESET.

GET_DEVICE_ID (bRequest = 0)

This class-specific request returns a device ID string that is compatible with IEEE 1284. See IEEE 1284

for syntax and formatting information. A printer with multiple configurations, interfaces, or alternate

settings may contain multiple IEEE 1284 device ID strings. The wValue field is used to specify a zero-

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