Datasheet

PIC18F97J94 FAMILY
DS30575A-page 530  2012 Microchip Technology Inc.
27.2.2.2 Internal Pull-up Resistors
The PIC18F97J94 family devices have built-in pull-up
resistors, designed to meet the requirements for low-
speed and full-speed USB. The UPUEN bit (UCFG<4>)
enables the internal pull-ups. Figure 27-1 shows the
pull-ups and their control.
27.2.2.3 External Pull-up Resistors
External pull-ups may also be used. The VUSB3V3 pin
may be used to pull up D+ or D-. The pull-up resistor
must be 1.5 k (±5%) as required by the USB
specifications.
Figure 27-2 provides an example of external circuitry.
FIGURE 27-2: EXTERNAL CIRCUITRY
27.2.2.4 Ping-Pong Buffer Configuration
The usage of ping-pong buffers is configured using the
PPB<1:0> bits. Refer to Section 27.4.4 “Ping-Pong
Buffering” for a complete explanation of the ping-pong
buffers.
27.2.2.5 Eye Pattern Test Enable
An automatic eye pattern test can be generated by the
module when the UCFG<7> bit is set. The eye pattern
output will be observable based on module settings,
meaning that the user is first responsible for configuring
the SIE clock settings, pull-up resistor and Transceiver
mode. In addition, the module has to be enabled.
Once UTEYE is set, the module emulates a switch from
a receive to transmit state and will start transmitting a
J-K-J-K bit sequence (K-J-K-J for full speed). The
sequence will be repeated indefinitely while the Eye
Pattern Test mode is enabled.
Note that this bit should never be set while the module
is connected to an actual USB system. This Test mode
is intended for board verification to aid with USB certi-
fication tests. It is intended to show a system developer
the noise integrity of the USB signals which can be
affected by board traces, impedance mismatches and
proximity to other system components. It does not
properly test the transition from a receive to a transmit
state. Although the eye pattern is not meant to replace
the more complex USB certification test, it should aid
during first order system debugging.
Note: A compliant USB device should never
source any current onto the +5V V
BUS line
of the USB cable. Additionally, USB
devices should not source any current on
the D+ and D- data lines whenever the
+5V VBUS line is less than 1.17V. In order
to be USB compliant, applications which
are not purely bus-powered should moni-
tor the V
BUS line, and avoid turning on the
USB module and the D+ or D- pull-up
resistor until V
BUS is greater than 1.17V.
V
BUS can be connected to and monitored
by a 5V tolerant I/O pin, or if a resistive
divider is used, by an analog capable pin.
PIC
®
MCU
Host
Controller/HUB
V
USB3V3
D+
D-
Note: The above setting shows a typical connection
for a full-speed configuration using an on-chip
regulator and an external pull-up resistor.
1.5 k