PIC18F-LF1XK50 MICROCHIP [Microchip Technology], PIC18F-LF1XK50 Datasheet - Page 253

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

The PPBRST bit (UCON<6>) controls the Reset status
when Double-Buffering mode (ping-pong buffering) is
used. When the PPBRST bit is set, all Ping-Pong Buf-
fer Pointers are set to the Even buffers. PPBRST has
to be cleared by firmware. This bit is ignored in buffer-
ing modes not using ping-pong buffering.
The PKTDIS bit (UCON<4>) is a flag indicating that the
SIE has disabled packet transmission and reception.
This bit is set by the SIE when a SETUP token is
received to allow setup processing. This bit cannot be
set by the microcontroller, only cleared; clearing it
allows the SIE to continue transmission and/or
reception. Any pending events within the Buffer
Descriptor Table will still be available, indicated within
the USTAT register’s FIFO buffer.
The RESUME bit (UCON<2>) allows the peripheral to
perform a remote wake-up by executing Resume
signaling. To generate a valid remote wake-up,
firmware must set RESUME for 10 ms and then clear
the bit. For more information on “resume signaling”,
see the “Universal Serial Bus Specification
Revision 2.0”.
The SUSPND bit (UCON<1>) places the module and
supporting circuitry in a Low-Power mode. The input
clock to the SIE is also disabled. This bit should be set
by the software in response to an IDLEIF interrupt. It
should be reset by the microcontroller firmware after an
ACTVIF interrupt is observed. When this bit is active,
the device remains attached to the bus but the trans-
ceiver outputs remain Idle. The voltage on the V
may vary depending on the value of this bit. Setting this
bit before a IDLEIF request will result in unpredictable
bus behavior.
 2010 Microchip Technology Inc.
Note:
While in Suspend mode, a typical
bus-powered USB device is limited to
500 A of current. This is the complete
current which may be drawn by the PIC
device and its supporting circuitry. Care
should be taken to assure minimum
current draw when the device enters
Suspend mode.
USB
Preliminary
pin
22.2.2
Prior to communicating over USB, the module’s
associated internal and/or external hardware must be
configured. Most of the configuration is performed with
the UCFG register
contains most of the bits that control the system level
behavior of the USB module. These include:
• Bus Speed (full speed versus low speed)
• On-Chip Pull-up Resistor Enable
• Ping-Pong Buffer Usage
The UTEYE bit, UCFG<7>, enables eye pattern gener-
ation, which aids in module testing, debugging and
USB certifications.
22.2.2.1
The USB peripheral has a built-in, USB 2.0, full-speed
and low-speed capable transceiver, internally con-
nected to the SIE. This feature is useful for low-cost,
single chip applications. Enabling the USB module
(USBEN = 1) will also enable the internal transceiver.
The FSEN bit (UCFG<2>) controls the transceiver
speed; setting the bit enables full-speed operation.
The on-chip USB pull-up resistors are controlled by the
UPUEN bit (UCFG<4>). They can only be selected
when the on-chip transceiver is enabled.
The internal USB transceiver obtains power from the
V
specifications, V
source between 3.0V and 3.6V. The best electrical
signal quality is obtained when a 3.3V supply is used
and locally bypassed with a high quality ceramic
capacitor. The capacitor should be placed as close as
possible to the V
edge of the package (i.e., route ground of the capacitor
to V
packaged parts).
The D+ and D- signal lines can be routed directly to
their respective pins on the USB connector or cable (for
hard-wired applications). No additional resistors,
capacitors, or magnetic components are required as
the D+ and D- drivers have controlled slew rate and
output impedance intended to match with the
characteristic impedance of the USB cable.
In order to meet the USB specifications, the traces
should be less than 30 cm long. Ideally, these traces
should be designed to have a characteristic impedance
matching that of the USB cable.
USB
Note:
SS
pin. In order to meet USB signalling level
pin 20 on 20-lead PDIP, SOIC, SSOP and QFN
PIC18F/LF1XK50
USB CONFIGURATION REGISTER
(UCFG)
The USB speed, transceiver and pull-up
should only be configured during the mod-
ule setup phase. It is not recommended to
switch these settings while the module is
enabled.
Internal Transceiver
USB
USB
(Register
must be supplied with a voltage
and V
SS
22-2).The UFCG register
pins found on the same
DS41350E-page 253