Microchip Technology MA180021 Manuale Utente
PIC18F87J50 FS USB Plug-In Module User’s Guide
DS51678A-page 14
© 2007 Microchip Technology Inc.
In addition to providing a convenient location for installing a digital current meter, JP4
also serves another purpose. In some cases, it may be undesirable to consume power
from the USB port, for example, when developing end applications that are always
self-powered or consume more than 300 mA (the maximum rating for the regulator). In
these cases, jumper cap, JP4, can be removed, and the PIM can obtain power from the
HPC Explorer board or directly from the test points.
Diode, D2, prevents the PIM from ever sourcing current onto the +5V V
also serves another purpose. In some cases, it may be undesirable to consume power
from the USB port, for example, when developing end applications that are always
self-powered or consume more than 300 mA (the maximum rating for the regulator). In
these cases, jumper cap, JP4, can be removed, and the PIM can obtain power from the
HPC Explorer board or directly from the test points.
Diode, D2, prevents the PIM from ever sourcing current onto the +5V V
BUS
pin of the
USB cable. The USB 2.0 specifications require that USB peripherals should never
source current onto the +5V V
source current onto the +5V V
BUS
line under any condition.
3.5
LEDs
Two high-efficiency, red LEDs have been included on the PIM. The LEDs are
connected to I/O pins, RE0 and RE1, and may be used for general purpose indication.
The LEDs are connected such that they turn on when the I/O pin controlling them is
driven high. Alternatively, if the I/O pin loading is undesirable (each LED consumes
approximately 1 mA when turned on), jumper cap covering, JP5, may be removed. This
will effectively disconnect both LEDs from their respective I/O pins.
connected to I/O pins, RE0 and RE1, and may be used for general purpose indication.
The LEDs are connected such that they turn on when the I/O pin controlling them is
driven high. Alternatively, if the I/O pin loading is undesirable (each LED consumes
approximately 1 mA when turned on), jumper cap covering, JP5, may be removed. This
will effectively disconnect both LEDs from their respective I/O pins.
3.6
PUSH BUTTONS
Two miniature push buttons are included on the PIM. Switch, S3 on the PIM, connects
to MCLR. It may be used to reset the microcontroller when the PIM is used either
stand-alone or while connected to the HPC Explorer board.
Pin, RB4 on the PIC18F87J50 microcontroller, is pulled up to V
to MCLR. It may be used to reset the microcontroller when the PIM is used either
stand-alone or while connected to the HPC Explorer board.
Pin, RB4 on the PIC18F87J50 microcontroller, is pulled up to V
DD
through a 15 kOhm
resistor (R26 on the PIM). If push button, S4 on the PIM, is pressed, it will pull RB4 low.
This push button may be used for any general purpose user interfacing purposes.
When the PIM is plugged into the HPC Explorer board, the RB0 push button on the
HPC Explorer will also work and can be used for additional general purpose user input.
This push button may be used for any general purpose user interfacing purposes.
When the PIM is plugged into the HPC Explorer board, the RB0 push button on the
HPC Explorer will also work and can be used for additional general purpose user input.
3.7
JUMPERS
The PIM has three jumper headers on it to provide additional flexibility for
experimentation and development purposes.
JP1 – This is a three-pin header with the labels, ‘I’, ‘R’ and ‘U’. The ‘R’ is an abbreviation
referring to microcontroller pin, RB5. ‘I’ is an abbreviation referring to the “ICE” female
header pin for the RB5 signal. ‘U’ is an abbreviation for the USB V
experimentation and development purposes.
JP1 – This is a three-pin header with the labels, ‘I’, ‘R’ and ‘U’. The ‘R’ is an abbreviation
referring to microcontroller pin, RB5. ‘I’ is an abbreviation referring to the “ICE” female
header pin for the RB5 signal. ‘U’ is an abbreviation for the USB V
BUS
line.
When the jumper is in the ‘R’ to ‘I’ position, the RB5 pin connects only to the ICE female
header pin, just like most of the other general purpose I/O pins. When the jumper is in
the ‘R’ to ‘U’ position, RB5 (which is 5.5V tolerant) can be used to sense when the USB
cable has been attached to the host, and when the host is actively providing power to
the +5V V
header pin, just like most of the other general purpose I/O pins. When the jumper is in
the ‘R’ to ‘U’ position, RB5 (which is 5.5V tolerant) can be used to sense when the USB
cable has been attached to the host, and when the host is actively providing power to
the +5V V
BUS
line. According to the USB 2.0 specifications, no device should ever pull
the D+ or D- lines high (such as with the D+ or D- pull-up resistor) until the host actively
powers the +5V V
powers the +5V V
BUS
line. This is intended to prevent self-powered peripherals from
ever sourcing even small amounts of power to the host when the host is not powered.
Small amounts of current could potentially prevent the host (and possibly other USB
peripherals connected to that host) from fully becoming depowered, which may cause
problems during power-up and initialization.
Small amounts of current could potentially prevent the host (and possibly other USB
peripherals connected to that host) from fully becoming depowered, which may cause
problems during power-up and initialization.