Board Hardware
©
2009 Microchip Technology Inc.
DS51806A-page 12
The JP2 jumper allows the microcontroller firmware to monitor the
USB_ATTACH
signal
when the jumper cap is in the position, R - U.
The resistors, R15 and R17 of the schematics (see
Appendix B. “Board Schematics”
),
serve multiple purposes. They level shift the +5V signal, provide a weak pull-down function
on the V
BUS
line (to oppose any leakage that would interfere with measuring V
BUS
in the
off/low state) and improve the ESD robustness of the circuit.
Peripherals that are purely bus-powered obtain all of their power directly from the +5V
V
BUS
line itself. For these types of devices, it is unnecessary to monitor when the V
BUS
is powered as the peripheral will not be able to source current on the D+, D- or V
BUS
lines when the host is not powered.
2.4.2
JP3 Jumper
If the PIC18F46J50 Full-Speed USB Demonstration Board is used as a stand-alone
device, it obtains its power from the USB cable. This requires jumper cap, JP3, to be
installed, since the jumper is in series with the power supply from the +5V V
BUS
pin
from the USB connector.
If the jumper cap is removed from JP3, a current meter can be connected across the
header to measure the current consumption from the USB cable. This enables
measurement of the total USB +5V V
BUS
current consumption, which is useful in
developing USB devices to meet USB compliance specifications.
The current consumption measured at the JP3 header will include the quiescent cur-
rent of the linear regulator, Q1, temperature sensor, U1, and the microcontroller, as well
as any leakage due to other circuitry on the board.
2.5
PROGRAMMING THE MICROCONTROLLER
The PIC18F46J50 Full-Speed USB Demonstration Board is too small to have the
full-sized RJ-11 jack normally used to connect to Microchip In-Circuit Serial Program-
ming™ (ICSP™) programmers. Instead, the board has a six-pin ICSP header (J4) that
can be used as the connection for reprogramming the microcontroller.
The PICkit™ 2 ICSP programmer can be connected directly to the J4 header.
Alternately, the six-pin, ICSP to RJ-11 adapter board, included with the board, can be
used to reprogram the microcontroller with other RJ-11 based programmers. Examples
of ICSP programmers that are supported (at the time this document’s publication)
include the MPLAB
®
In-Circuit Debugger, ICD 2 and ICD 3, and the In-Circuit Emulator,
REAL ICE™.
When connecting to the six-pin header, ensure that the polarity and alignment are
correct. For reference, the board’s silk screen denotes pin 1 of the header (MCLR) with
an arrow and has a square surrounding the pin.
The RJ-11 to ICSP adapter board also provides a reference on its silk screen with a
square around the MCLR pin. When the adapter board connects correctly to the
demonstration board, the two square markings are aligned with each other.
If the PIC18F46J50 Full-Speed USB Demonstration Board is being used with the
PIC18 Explorer Board or PICDEM HPC Explorer Board, the board’s RJ-11 jack can
also be used to reprogram or debug the PIC18F46J50.
