e00a022.pdf

BASI CS

The Universal Serial Bus

Part 2: Transfers and Drivers

By B. Kainka

In the ﬁrst part of this article we looked at the electrical characteristics

of the USB standard. In this part we investigate the software and protocols

used with this interface. Also included is a practical programming example.

When any new device is first

plugged in to the USB connector, it

will signal its presence to the hub by

pulling up one of the two data wires

of the USB cable. Next comes the fol-

lowing sequence of events:

- The hub indicates to the host that a

new device has been connected to

the bus.

- The host will ask the hub which

port the device will use.

- Now the host knows which port

the device will use, it enables the

port and issues a bus reset com-

mand to the hub.

- The hub generates a reset signal on

the bus by pulling both data lines

D+ and D- low for 10 ms. After

reset, the device is ready and will

respond using the default address 0.

- Until the device is assigned its own

bus address it will use the default

address. The host will read the ﬁrst

bytes of the device descriptor to

determine the length of the data

packet in order to assign a length

to the default pipe.

- The host will allocate a bus address

to the device.

- The host will now read all the con-

figuration information from the

device using its newly allocated

bus address.

- The host assigns one of the possible

configurations to the device. The

current consumption of the device

Elektor Electronics

10/2000

(USB)

BASI CS

Figure 1. Screen shot of the USB

Thermostat.

Figure 2. Mini hardware driver for the

Heater Controller.

must not be more than that deﬁned

in its conﬁguration descriptor. The

device is now ready for use.

down this road you can probably see

that eventually the whole ‘Plug and

Play’ concept would be undermined

by device manufacturers assigning

themselves identical VID’s leading

to all sorts of confusion.

For our purposes, the best (and

perfectly legal) solution is to use the

vendor ID of the semiconductor man-

ufacturer corresponding to the USB

chip in the device. A device incorpo-

rating the USB Soundchip UDA1321

would use the VID of its manufac-

turer i.e. Philips. For the EZ USB Chip

from Anchor you will use the Anchor

driver and your own software in the

controller.

information that requires error protection but

is not time critical. Typical applications for

this method of data transfer would be pass-

ing data to a printer or receiving data from a

scanner. The actual data rate is adapted to

the capacity of the USB system. This method

has a low priority.

- Isochronous-Transfer

Devices transferring large amounts of infor-

mation at a defined data rate, e.g. digitised

audio to a soundcard, would use this transfer

method. A defined data rate is guaranteed

but no error protection is included. With these

devices, occasional errors are less important

than gaps in the data.

The microcontroller in the USB

device responds to each message

from the host. A hardware interrupt

will indicate that data has been

received and is available in FIFO 0.

The data is analysed to determine

what type of message it is. Key

bytes in the data packet request the

device descriptor. The microcon-

troller will respond by reading the

requested information from its ROM

and writing it to its output FIFO.

From there it will be sent back to the

master. The ﬁrst descriptor sent will

be the device descriptor which has a

length of 18 bytes. The host will ini-

tially take the ﬁrst 8 bytes. After the

host has assigned the device

address, it will read the rest of the

descriptor. The 18 data bytes will be

spread over three frames to enable it

to ﬁt into the 8 byte FIFO.

Table 1 shows the Device

Descriptor of the USB Thermometer

from Cypress, which was featured in

part 1 of this series. Each device

requires a Vendor-ID and a device ID.

Using these numbers, the device is

recognised and the corresponding

driver software is loaded from the

host to the device. The Vendor-ID is

assigned under license to a device

manufacturer by the USB Organisa-

tion. Those who intend to make a

serious business of developing USB

devices must also arrange for their

own vendor ID.

For the hobbyist it is in theory

possible to unofficially make up your

own VID. This will entail writing

your own driver and a .INF file to

conﬁgure the device. If we carried on

Low-speed devices support control and Inter-

rupt Transfer modes while full speed devices

support all four modes. For use in the area of

control, measurement and regulation the con-

trol transfer method is particularly useful, it

offers high data rate together with data error

protection. The communication protocol is

comparatively easy to implement for this

application so for our purposes here we will

use the control transfer method for the Elek-

tor Electronics USB Interface.

Types of USB Transfer

There are currently four completely

different methods of communicating

between a USB device and a PC:

- Control-Transfer

Used for control signals to the

device, they have a high priority and

incorporate automatic error protec-

tion. Data rate is high and up to

64 Bytes per request can be sent.

- Interrupt-Transfer

Devices such as keyboards and mice

would generally use this method.

These devices send small amounts

of data periodically to the PC. The

name of this transfer would suggest

that a hardware interrupt is respon-

sible for the data ﬂow but this is not

the case, nor is it possible in a single

master system. Actually, the system

looks for new data every 10 ms or so.

The amount of data sent using this

transfer would typically be up to

eight bytes at a time.

- Bulk-Transfer

Used to transfer large amounts of

Control Transfers in Delphi

Software drivers are used to control USB

devices. Conventional methods of controlling

PC peripherals via their hardware port

addresses using DOS are no longer possible

with the USB interface. In order to control a

device it is necessary to study the documen-

tation of the driver function.

Drivers are in principle treated as data

ﬁles. They are opened, you can read or write

data to them and then they are closed. Pro-

gramming is very akin to accessing data or

passing data to and from the RS232 interface.

For example, writing to a USB printer

would be performed with WriteFile while

reading data from a USB scanner would be

performed with ReadFile. In this example of

10/2000

Elektor Electronics

BASI CS

USB Controllers

- 5 V supply with internal 3.3V voltage regulator.

- SSC (SPI) interface

- 8 K OTP

- external up to 64 K RAM and ROM

- Package outline: PLCC 44, PSDIP 52

When starting in USB development, it is a good idea to choose a

USB family, i.e., a microcontroller and/or programming tools

(Assembler or C compiler), which you are already familiar with

and which is readily available. Equally important is the amount and

quality of the supplied documentation. Some companies produce

Starter Kits that come complete with volumes of software docu-

mentation

Cypress

www.cypress.com

Cypress supply the low cost, low speed CY7C63000 Family controller,

mainly intended for HID’s. The CY7C63001 is used in the Elektor-Elec-

tronics Interface. One advantage for developers is the PDIP package out-

line. Cypress provides documentation for different ‘reference designs’

which makes development easier.

Philips Semiconductors

http://www.semiconductor.philips.com

Produce two interesting full speed-USB-Transceivers. These are similar to

a UART and can be easily used in existing microcontroller systems or can

be interfaced to most microcontrollers.

- Low speed USB

- 1 Control endpoint, 1 Interrupt endpoint. (per 8 Bytes)

- 8 Bit RISC-Processor

- 6 MHz crystal, internal clock 12 MHz.

- 128 bytes of RAM

- 2K OTP (CY7C63000A)

- 4K OTP (CY7C63001A)

- Programmable current output port with a 4 Bit D/A

- Package outline: PDIP 20, SOIC 20

The PDIUSBD11 with only 16 pins uses an I 2 C-Bus-Interface for easy

connection to a microcontroller. The chip contains 4 end points and two

8-bit FIFOS for In- and Out-transfers.

- Full speed-USB

-I 2 C Bus Interface up to 1 Mbit/s

- 12 MHz crystal, multiplied to 48 MHz internally using a PLL.

- 1 Control, 6 generic endpoints (8 Bit Max Packet Size)

- Package outline: DIP-16 and SO-16

The PDIUSBD12 is a full-speed USB-Transceiver with a parallel interface

compatible with an 8051 Controller. It has three endpoints, which can hold

from 1 to 128 bytes. The package has 28 pins but is unfortunately only avail-

able for SMD mounting.

Motorola

http://sps.motorola.com

Friends of the HC05-Family are not left out. Motorola produce the

68HC705JB3 low-speed USB Controller with 2 Interrupt endpoints. The

68HC705JB4 also has an A/D converter.

- Full-speed USB

- Parallel Data bus with data rate up to 2 Mbytes/s

- DMA support

- Up to 1MByte/s in Bulk Mode

- Up to 1Mbit/s in Isochronous Mode

- 1 Control, 4 Generic (Dependent on Mode)

- 320 Bytes (in total) deep FIFO

- On board 3.3 V voltage regulator

- Package outline: SO28 and TSSOP28

- Low speed USB 68HC705JB3

- HC05 core.

- 2560 Bytes User ROM

- 144 Bytes RAM

- Low Speed 1.5Mbps

- 1 Control, 2 Interrupt endpoints

- Package outline: PDIP-20/28 and SOIC

AnchorChips

www.anchorchips.com

The AN2131 is a versatile USB-Controller with a 8051 compatible core.

The in-built USB Machine is capable of self-enumeration. With this con-

troller you can build a USB device without writing a single line of code.

The chip announces itself as an Anchor Default Interface and has all the

functions and further program code for loading and starting. This simpliﬁes

the development in the controller. Program download via USB means an

end to the annoying burn/wipe EPROM cycle normally associated with

program development.

- Low speed USB 68HC705JB4

- HC05 core

- 3584 Bytes ROM

- 176 Bytes RAM

- 1 Control, 2 Interrupt endpoints

- 6 channel, 8 Bit A/D converter

- Package outline: PDIP 28 and SOIC 28

- Full speed USB

- 12 MHz crystal, multiplied to 48 MHz internally using a PLL

- 8051 Core.

- Programme Download using USB.

-I 2 C interface

- 8 K internal RAM, expandable to 64 K externally.

- Package outline: PQFP-44, PQFP-80

Microchip

http://www.microchip.com

If you prefer PIC controllers, Microchip produce these low-speed USB

controllers. They include an A/D converter and a serial interface UART.

PIC16C745

- Low speed USB with 6 endpoints

- 8 Bit A/D converter, 5 Inputs

- 8k Program Memory

- UART

- Package outline: PDIP 20

Inﬁneon

http://www.inﬁneon.de

Produces the C541U, an 8051 compatible full speed Controller. The pri-

mary application for this controller is intended to be telecommunications

e.g. ISDN modems. The controller has external RAM and program mem-

ory that simpliﬁes development.

PIC16C765

- Low speed USB with 6 endpoints

- 8 Bit A/D converter, 8 inputs

- 8k Program Memory

- UART

- Package outline: PDIP 40

- Full speed USB, selectable low speed

- 12 MHz crystal

- 8051 core (C500)

Elektor Electronics

10/2000

BASI CS

unit USB1;

interface

uses Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,

ExtCtrls, StdCtrls;

type

TForm1 = class(TForm)

Timer1: TTimer;

Edit1: TEdit;

procedure FormCreate(Sender: TObject);

procedure Timer1Timer(Sender: TObject);

end;

type _lIn = record

bFunction : Byte;

bValue1 : Byte;

bValue2 : Byte;

bValue3 : Byte;

end;

type _lOut = record

bAck : Byte;

bValue1 : Byte;

bValue2 : Byte;

bValue3 : Byte;

end;

var

Form1: TForm1;

Temp : Real;

implementation

{$R *.DFM}

procedure Thermo;

var lIn: _lIn;

lOut: _lOut;

DeviceHandle: THandle;

TemplateHandle: THandle;

nBytes: DWord;

bresult: Boolean;

begin

DeviceHandle := CreateFile

(‘\\.\Thermometer_0’,Generic_write,File_Share_write,nil,open_existing,0,TemplateHandle);

lIn.bFunction := 11; {Read Thermometer}

bResult := DeviceIoControl(DeviceHandle,$04,@lIn,sizeof(lIn),@lOut,sizeof (lOut),nBytes,nil);

Temp := lOut.bValue1/2;

lIn.bFunction := 23; {Write RAM}

lIn.bValue1 := 47; {Adr. 47 = Port 1}

if Temp > 37 then lIn.bValue2 := 0 else lIn.bValue2 := 15;

bResult := DeviceIoControl(DeviceHandle,$04,@lIn,sizeof(lIn),@lOut,sizeof (lOut),nBytes,nil);

CloseHandle (DeviceHandle);

end;

procedure TForm1.FormCreate(Sender: TObject);

begin

Timer1.Interval := 100;

Timer1.Enabled := true;

end;

procedure TForm1.Timer1Timer(Sender: TObject);

begin

Thermo;

Edit1.Text := FloatToStrF(Temp,ffGeneral,3,2) + ‘°C’;

end;

end.

Listing 1. Control access in Delphi.

10/2000

Elektor Electronics

BASI CS

Table 1. Format of the Device Descriptors

Fieldname

Length(in bytes), Description

Example

Blength

1, length of the Descriptor in Bytes

12h

BDescriptorType

1, Descriptor type (01h=Device Descriptor)

01h

BcdUSB

2, USB Version (V. 1.0)

00h, 01h

BDeviceClass

1, Class Code

00h

BDeviceSubClass

1, Subclass Code

00h

BDeviceProtoco

1, Protocol Code

00h

bMaxPacketSize0

1, EP0-FIFO size

08h

IdVendor

2, Vendor ID (04B4h=Cypress)

B4h, 04h

IdProduct

2, Product ID (02=Thermometer)

02h, 00h

BcdDevice

2, Version number (V.09)

09h, 00h

IManufacturer

1, String Index for “manufacturer”

01h

Product

1, String Index for “Product”

02h

ISerialNumber

1, String Index for “Serial number”

00h

BNumConﬁgurations

1, The number of possible conﬁgurations

01h

a printer, data will only be flowing in one

direction so the USB bulk transfer method

would be employed — control transfer would

not be suitable here because it allocates time

for data to ﬂow in both directions.

For control transfer methods the Windows

function DeviceIoControl is used. Listing 1

shows the Delphi program that reads the

temperature from the Elektor Electronics

interface. The Windows Function CreateFile

supplies a Handle to the device or rather its

driver. The device name \\.\Thermometer_0

is deﬁned in the driver. With the valid handle,

it will access the temperature reading. Lastly

the device will be closed with CloseHandle.

All these three Windows functions are

declared in the Delphi 4 Windows unit. For

more precise information, see Windows.pas

and further information is in the help file

WIN32.HLP.

Each access with DeviceIoControl requires

a control code that is used to call one of the

possible driver functions. Additionally two

buffers need to be initialised, one input buffer

and one output buffer. Both buffers require a

maximum length of four bytes. In the listing,

these buffers are deﬁned as byte records. The

ﬂow direction of the data in the buffers is not

defined, and a driver could use both buffers

to send data in the same direction. In our

example 1In sends data to the USB controller,

while 1Out receives data from the device.

To read the temperature, the value 11 (or

0Bhex) is sent as the first byte to the in

buffer — this is done in the lIn.bFunction.

The following positions bValue1 to bValue2

are used by the Read Thermometer

function, not by the driver. If every-

thing works correctly, the driver will

return four bytes in lOut. The driver

status indication is contained in

bAck (1 indicates success). bValue1

contains the temperature, bValue2

the sign of the temperature value

and bValue3 is the status of the

pushbuttons.

This example program imple-

ments a thermostat to maintain a

temperature of 37°C (ideal for incu-

bating chicken eggs!). The output

appears on the four output lines of

Port 1 together with the green LED.

While the Function 11 reads the

temperature, Function 23 writes to a

RAM address in the controller. Using

Address 47, the Elektor Electronics

firmware allows access to port 1.

After each temperature measure-

ment, a value of either 15 (all 1’s) or

00 (all 0’s) will be sent out depend-

ing on whether the temperature is

too high or too low. To control the

heater, a Power FET type BUZ10 can

be used at the output to switch the

current ( Figure 2 ). For test purposes

a 100-

be downloaded from the author’s

homepage:

http://home.t-online.de/home/

B.Kainka

The USB Driver

resistor (physically in con-

tact with the temperature sensor)

will serve as the heating element.

Using a supply voltage of 5 V it will

be possible for the resistor to reach

the selected temperature.

The complete Delphi Program can

Ω

Developers of USB devices can write

the necessary device driver or they

can build a device which already has

an existing class driver. This option

is however not available for applica-

tions of control, measurement and

regulation. The necessary prerequi-

sites for developing a USB driver are

C++ development environment and

the Driver Development Kit (DDK)

from Microsoft. This kit includes an

example USB driver together with

helpful additional information. Writ-

ing your own driver is however not a

trivial exercise, so the more exam-

ples of driver code you can study, the

better. Included along with the EZ-

USB Starter kit from Anchor Chips is

the complete source code for a ver-

satile USB driver. Also worth a visit

for a good introduction to USB is the

website run by Craig Peacock

( www.beyondlogic.org ). He has also

written a driver for the USB ther-

mometer that can be used with the

Elektor Electronics interface.

(000094-2)

Elektor Electronics

10/2000

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika: