PIC18F-LF1XK50 MICROCHIP [Microchip Technology], PIC18F-LF1XK50 Datasheet - Page 255

• Manufacturer Part Number: PIC18F-LF1XK50
• Description: 20-Pin USB Flash Microcontrollers
• Manufacturer: MICROCHIP [Microchip Technology]

22.2.2.2
The PIC18F1XK50/PIC18LF1XK50 devices have
built-in pull-up resistors designed to meet the require-
ments for low-speed and full-speed USB. The UPUEN
bit
Figure 22-1
22.2.2.3
External pull-up may also be used. The V
used to pull up D+ or D-. The pull-up resistor must be
1.5 k (±5%) as required by the USB specifications.
Figure 22-2
FIGURE 22-2:
 2010 Microchip Technology Inc.
Note:
Note:
Microcontroller
(UCFG<4>)
PIC
The above setting shows a typical connection
for a full-speed configuration using an on-chip
regulator and an external pull-up resistor.
The official USB specifications require
that USB devices must never source any
current onto the +5V V
cable. Additionally, USB devices must
never source any current on the D+ and
D- data lines whenever the +5V V
is less than 1.17V. In order to meet this
requirement, applications which are not
purely bus powered should monitor the
V
module and the D+ or D- pull-up resistor
until V
be connected to and monitored by any 5V
tolerant I/O pin for this purpose.
shows an example.
shows the pull-ups and their control.
®
BUS
Internal Pull-up Resistors
External Pull-up Resistors
V
USB
D+
D-
line and avoid turning on the USB
BUS
enables
is greater than 1.17V. V
EXTERNAL CIRCUITRY
1.5 k
the
BUS
Controller/HUB
internal
line of the USB
USB
Host
pin may be
BUS
BUS
pull-ups.
can
line
Preliminary
22.2.2.4
The usage of ping-pong buffers is configured using the
PPB<1:0> bits. Refer to
Buffering”
buffers.
22.2.2.5
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.
PIC18F/LF1XK50
for a complete explanation of the ping-pong
Ping-Pong Buffer Configuration
Eye Pattern Test Enable
Section 22.4.4 “Ping-Pong
DS41350E-page 255