e009044.pdf

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USB Interface

Experimenting with the Universal Serial Bus

Design by B. Kainka

Everybody is talking about the USB. In the long term, this new serial

interface could replace many of the PC interfaces that have been used up

to now. This is reason enough for looking at it more closely.

Before getting into practical details, let’s ﬁrst

look at the basic features of the Universal Ser-

ial Bus. In USB Version 1.0, there are

‘lowspeed’ devices with a data rate of

1.5 Mb/s, and ‘fullspeed’ devices with a data

rate of 12 Mb/s. Even the lower data transfer

rate is several times faster than the possible

baud rates of a serial interface.

Up to now, we have often been faced with

unpleasant situations in which all of the PC

interfaces are already in use. The

advantage of the USB here is that

you can always make four new ports

available by connecting a supple-

mentary bus distributor (hub). Up to

127 devices in total can be con-

nected to the bus.

The USB connection also provides

the operating voltage for small

devices. Up to 100 mA can be drawn

from the interface without any spe-

cial provisions. With a special

demand login, this can be increased

to 500 mA. Typical laboratory appli-

cations often need signiﬁcantly less

than this. Eliminating the extra

power cable for each device helps in

the struggle against the general

‘cable salad’.

USB devices can always be con-

nected and disconnected while the

system is operating. The operating

system automatically loads the nec-

essary driver. This extended Plug-

and-Play capability considerably

simplifies working with multiple

devices. A bus number is automati-

cally assigned to each newly con-

nected device (enumeration). The

operating system first reads a cer-

tain amount of information from the

device and then automatically loads

a suitable driver.

This means that every USB device

is already signiﬁcantly more intelli-

gent than a device with an RS232

interface. It must make itself known

to the operating system by means of

a series of description tables (descrip-

tors), in order that the correct driver

can be selected. With the very ﬁrst

connection, the operating system

requests a diskette with the driver.

For all subsequent reconnections, the

driver is loaded automatically, so that

the user does not have to take any

action. If the device is disconnected

from the PC, the driver is automati-

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cally deleted from memory.

Unfortunately, USB can presently be

used only with PCs that use the Win-

dows 98 operating system. Although

USB can in principle be used under

Windows 95 from version SR2

onwards, this is not completely reli-

able. Consequently, Windows 98 is

recommended for use with the USB

Interface. Windows NT5 and Win-

dows 2000 support USB, but Win-

dows NT4 does not support USB at

all. However, the software for this

project has not been tested with

Windows 2000.

6 MHz

RESONATOR

R/C EXT

CY7C63001

OSC

INSTANT-ON

NOW TM

RAM

128 Byte

8-bit

Timer

EPROM

2K/4K Byte

RAM

128 Byte

Power

Reset

Interupt

Controller

USB

Engine

PORT

Watch

Dog

Timer

The circuit

D+, D-

V CC / V SS

P0.0 - P0.7

P1.0 - P1.3

000079 - 12

The USB Interface is based on the

Cypress CY7C6300 microcontroller.

This IC was primarily developed for

small USB devices, such as mice and

joystick ports, and it contains a com-

plete USB engine for the lowspeed

USB. The two data lines (D+ and D–)

are connected directly to the micro-

controller. Figure 1 shows the block

diagram of the IC. In addition to a

RISC processor, it contains an OTP

ROM for the operating software

(ﬁrmware) and two ports with a total

of twelve output lines, as well as

RAM and a timer.

The USB Interface presented here

is based on a Cypress application.

Cypress made their USB thermome-

ter available in the CY3640 starter

kit. This kit was intended mainly to

promote familiarity with the proces-

sor and the circuit technology. It is

no longer available in the original

form, but we have resurrected it in

this Elektor project. You can use the

USB Interface to get acquainted with

the USB, and you can also use it for

many different types of serious appli-

cations.

The USB Interface includes the

following functions:

Figure 1. Block diagram of the CY7C63001.

IC2

100n

CLK

D 1

D 2

RST

100n

DS1620

JP1

JP2

VCC

P0.0

P0.1

P0.2

P0.3

P0.4

P0.5

P0.6

P0.7

IC1

USB Type B

6MHz

CY7

D –

C63001

A CP

D +

P1.0

P1.1

P1.2

P1.3

CEXT

VSS VPP

– temperature measurement

– polling a pushbutton switch

– setting the brightness of a LED

000079 - 11

Figure 2. Complete schematic diagram of the USB Interface with temperature sensor.

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COMPONENTS LIST

000079-1

Resistors:

R1 = 47 Ω

R2 = 270 Ω

R3 = 10k Ω

R4 = 47 Ω

R5 = 1k Ω 5

JP2

Capacitors:

C1,C2 = 100nF

Semiconductors:

D1 = LED, red,

D2 = LED, green

IC1 = CY7C63001ACP

(programmed, order code

000079-41 )

IC2 = DS1620

JP1

Figure 4. Screen display of the original

Cypress demo program.

Figure 3. The USB Interface can be build using

this printed circuit board.

Miscellaneous:

JP1,JP2 = 2-way pinheader with

jumper

K1 = 10-way PCB terminal block

K2 = solder pin

K3 = USB socket, PCB mount,

type B (Farnell #153-503)

S1 = pushbutton 1 make contact

X1 = 6MHz ceramic resonator,

(Murata CSA6.00MG (Farnell #

295-292), or Newport

ZTA6.00MT

Enclosure: approx. size 61x22x80

mm (Conrad Electronics

#522848)

Project disk,

order code 000079-11

PCB, order code 000079-1

Figure 5. The program allows access

to all port functions of the

microcontroller, and also displays the

temperature.

– nine freely-accessible I/O ports

The pushbutton toggles an internal

program register, which can be

polled via the USB.

The two bus lines, D+ and D–, are

led to a Type B USB connector. If you

cannot come up with such a connec-

tor, you may solder the USB cable

directly to the circuit board. The USB

Interface takes its operating voltage

(+5 V and earth) from the bus. The

second (red) LED, D1, which should

be a low-power type, indicates the

presence of the supply voltage. This

voltage can also be used for other

purposes via the solder posts K2.

The 47-k

capacitors are already integrated

into the IC.

The USB Interface is fully compatible with the

original Cypress thermometer application.

This means that you can use all sample pro-

grams and the thermometer driver. However,

in the original application, the port accesses

were not fully functional. Consequently, the

firmware has been modified, and it also

includes additional functions.

Figure 2 shows the circuit diagram. The

temperature is sensed by a Dallas DS1620 IC,

which occupies three port lines (P0.0–P0.2).

The remaining nine lines (P0.3–P0.7 and

P1.0–P1.3) are led out to terminal strip K1, for

general use. In addition, a green LED (not a

low-current type!) can be connected to port

connection P1.3 via jumper JP1. This LED

indicates successful enumeration, and it can

be set to 16 different brightness levels. How-

ever, this works only if pushbutton switch S1

is connected to port P1.2 via jumper JP21.

Construction and testing

resistor ensures that no

more than the allowed 100 mA can

be drawn from the USB connection

in case of a short circuit.

The microcontroller is clocked by

a 6-MHz ceramic resonator with two

(and not three!) leads. The necessary

The construction of the small printed

circuit board shown in Figure 3

should not present any problems.

Sockets may be used for both ICs.

Once everything has been assem-

bled and there are no obvious con-

struction errors, there comes the

moment of truth. Connect the USB

Interface to a PC using a type A–B

USB cable. After a moment, Win-

dows will recognise that new hard-

ware has been connected. A win-

dow will appear with a request to

insert a diskette with a suitable dri-

ver. You can comply by inserting the

diskette labelled 000079-11 in drive

A. Here the system will ﬁnd the ﬁle

Ω

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Info on the Internet

Fahrenheit or Celsius degrees for the temper-

ature display. In addition, the brightness of

the green LED can be altered. The microcon-

troller includes a 4-bit D/A converter that can

be used to set the level of the current sunk by

the Port 1 outputs. However, the software

only allows Port P1.3 to be set. Figure 4

shows how the temperature is displayed on

the monitor.

Microsoft VB5

www.microsoft.com/msdownload/vbcce.htm

Cypress CY7C63001ACP microcontroller

http://www.cypress.com/cypress/prodgate/usb/cy7c63001.html

Dallas temperature sensor

http://www.dalsemi.com/datasheets/pdfs/1620.pdf

Programming

in Visual BASIC

An interface is not especially interesting if

you cannot drive it using your own programs.

You can access the device via a small Visual

BASIC program. We use V5BCCB, which

Microsoft allows to be downloaded free of

charge and which is fully functional, but

which cannot generate executable stand-

alone applications.

CypressSemiconductorsCYPRESS.INF

, which describes the device and the

driver. Following this, it loads the

actual driver USBTherm.sys . As soon

as this process is completed, the

device is enumerated, which means

that it is logged on to the system.

Now, not only the red LED is lit (if

JP2 is installed) but also the green

LED.

The Cypress demo software on

the diskette, Thermometer.exe ,

implements a thermometer with a

graphic display of temperature ver-

sus time. If JP1 is installed, the user

can use the keyboard to select

Listing 1. The USB1.BAS module with declarations

Attribute VB_Name = “Module1”

Type SECURITY_ATTRIBUTES

nLength As Long

lpSecurityDescriptor As Long

bInheritHandle As Long

End Type

Type OVERLAPPED

Internal As Long

InternalHigh As Long

offset As Long

OffsetHigh As Long

hEvent As Long

End Type

Declare Function CreateFile Lib “kernel32” Alias “CreateFileA”

(ByVal lpFileName As String, ByVal dwDesiredAccess As Long,

ByVal dwShareMode As Long, lpSecurityAttributes As SECURITY_ATTRIBUTES,

ByVal dwCreationDisposition As Long, ByVal dwFlagsAndAttributes As Long,

ByVal hTemplateFile As Long) As Long

Declare Function DeviceIoControl Lib “kernel32” (ByVal hDevice As Long,

ByVal dwIoControlCode As Long, lpInBuffer As Any, ByVal nInBufferSize

As Long, lpOutBuffer As Any, ByVal nOutBufferSize As Long,

lpBytesReturned As Long, lpOverlapped As OVERLAPPED) As Long

Declare Function CloseHandle Lib “kernel32” (ByVal hObject As Long) As Long

Public Security As SECURITY_ATTRIBUTES

Public gOverlapped As OVERLAPPED

Public hgDrvrHnd As Long

Public Const GENERIC_READ = &H80000000

Public Const GENERIC_WRITE = &H40000000

Public Const FILE_SHARE_WRITE = &H2

Public Const FILE_SHARE_READ = &H1

Public Const OPEN_EXISTING = &H3

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Listing 2. Accessing all ports and functions

Dim sFileName As String

Dim htemp As Long

Dim lIn As Long, lInSize As Long, lOut As Long, lOut-

Size As Long, lSize As Long

Dim lTemp As Long

Sub USB_IO()

sFileName = “\\.\Thermometer_0”

hgDrvrHnd = CreateFile(sFileName, GENERIC_WRITE Or

GENERIC_READ, FILE_SHARE_WRITE Or FILE_SHARE_READ,

Security, OPEN_EXISTING, 0, 0)

lTemp = DeviceIoControl(hgDrvrHnd, 4&, lIn, lInSize,

lOut, lOutSize, lSize, gOverlapped)

htemp = CloseHandle(hgDrvrHnd)

End Sub

USB_IO

End Sub

Private Sub HScroll1_Change()

Wert = HScroll1.Value * 8 + 7

WrRAM 46, Wert

Label4.Caption = Str$(Wert)

End Sub

Private Sub HScroll2_Change()

WrRAM 47, HScroll2.Value

Label5.Caption = HScroll2.Value

End Sub

Sub Brightness(Level)

lIn = Level * 256 + 14

lInSize = 2

lOutSize = 1

USB_IO

End Sub

Private Sub HScroll3_Change()

Brightness HScroll3.Value

Label6 = HScroll3.Value

End Sub

Private Sub Timer1_Timer()

lIn = 11

lInSize = 1

lOutSize = 3

USB_IO

Temp = ((lOut \ 256) And 255) / 2

Minus = (lOut \ 65536) And 255

If Minus > 0 Then Temp = Temp * -1

Button = (lOut \ 16777216) And 255

Label7.Caption = Str$(Temp)

Label8.Caption = Str$(Button)

Label9.Caption = Str$(RdPort(0))

Label10.Caption = Str$((RdPort(1)) And 15)

End Sub

Function RdPort(Port) As Integer

lIn = Port * 256 + 20

lInSize = 2

lOutSize = 2

USB_IO

RdPort = (lOut / 256) And 255

End Function

Sub WrRAM(Adresse, Wert)

lIn = 65536 * Wert + Adresse * 256 + 23

lInSize = 3

lOutSize = 1

Functions

15h: Write Port

lIn: Value (0-255), Port (0,1), 15h (Length: 3 Bytes)

iOut: Status (Length: 1 Byte)

0Bh: Read Thermometer

lIn: 0Bh (Länge: 1 Byte)

iOut: Button, Sign, Temp, Status (Length: 4 Bytes)

16h: Read RAM

lIn: Address (0-255), 16h (Length: 2 Bytes)

iOut: Value, Status (Length: 2 Bytes)

0Eh: Set LED Brightness

lIn: Brightness (0-15), 0Eh (Length: 2 Bytes)

iOut: Status (Length: 1 Byte)

17h: Write RAM

lIn: Value (0-255), Address (0-255), 17h (Length: 3 Bytes)

iOut: Status (Length: 1 Byte)

14h: Read Port

lIn: Port (0,1), 14h (Length: 2 Bytes)

iOut: Wert, Status (Length: 2 Bytes)

18h: Read ROM

lIn: Index, Address (0-255), 18h (Length: 3 Bytes)

iOut: Value, Status (Length: 2 Bytes)

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