External circuitry requirements, Figure 3 . external crystal connection, Figure 5 . self-powered device example connection – Lucent Technologies USS-720 User Manual

Page 50: Figure 6 . uss-720 connection to ieee 1284, Instant usb, Ieee, Uss-720, Preliminary data sheet, rev. 5 usb-to

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5-24

Lucent Technologies Inc.

USS-720

Instant USB

Preliminary Data Sheet, Rev. 5

USB-to-

IEEE

1284 Bridge

September 1999

13

External Circuitry Requirements

The USS-720 is intended to be a single-chip solution.
As such, the USB transceiver and the

IEEE 1284 buff-

ers have been integrated on-chip. External require-
ments include a 3.3 V supply and a 1.5 k

Ω ±

5% pull-up

resistor for the DPLS pin. If the internal oscillator is
used, a 12 MHz crystal along with bias capacitors are
needed (see Figure 3). If the internal oscillator is not
used, a 12 MHz clock signal should be supplied to
CLK_LO, and CLK_HI should be left unconnected.
1.2 k

Ω ±

5% pull-up resistors are needed on all

IEEE

1284 signals (except PLH), unless used in the High
Drive Mode (see the following page). A 5 V supply and
USB and/or

IEEE 1284 connectors might also be

needed, depending on the application.

Figure 3. External Crystal Connection

Figure 4 shows the normal USS-720 connection to the
USB. Both DPLS and DMNS require 24

Ω ±

1% series

resistors for USB impedance matching. Additionally, a
1.5 k

pull-up resistor is required on DPLS for full-

speed/low-speed differentiation.

Figure 4. USB Transceiver Connection

(Normal Mode)

For using the USS-720 in a self-powered device, there
are some additional considerations. The device must
refrain from supplying power through the pull-up
resistor when the device is plugged into an unpowered
bus. The USS-720 device circuit must also ensure that
the DPLS and DMNS lines are in an appropriate state
when the device is powered but not plugged in.
Figure 5 shows an example connection to meet these
requirements.

Figure 5. Self-Powered Device Example Connection

Figure 6 shows a USS-720-to-

IEEE 1284 parallel port

connection that complies with the

IEEE 1284 specifica-

tion. Other connections are also possible. While the
IEEE specification requires these resistors, developers
must make their own design decision against the
500

µ

A suspend mode current requirements required

by the USB specification.

Figure 6. USS-720 Connection to

IEEE 1284

5-5259.r2

CRYSTAL

12 MHz

CLK_LO

15 pF

CLK_HI

15 pF

TO INTERNAL

USS-720

TO INTERNAL

USS-720

5-5404.r1

+3.3 V V

DD

DPLS

DMNS

1.5 k

Ω ±

5%

24

Ω ±

1%

24

Ω ±

1%

5-5506a.r4

DPLS

DMNS

24

Ω ±

1%

24

Ω ±

1%

+3.3 V

1.5 M

SWITCH ON WHEN V

BUS

IS POWERED

1.5 k

Ω ±

5%

1.5 M

+5 V

PLH

7.5 k

Ω ±

5%

1.2 k

Ω ±

5%

ALL PARALLEL PORT
INPUT SIGNALS
EXCEPT PLH

+5 V

1.2 k

Ω ±

5%

ALL PARALLEL PORT
OUTPUT SIGNALS

24

Ω ±

5%

5-5505a.r1

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