Supporting USB - USB Mass Storage: Designing and Programming Devices and Embedded Hosts - page 39

Microchip PIC18F4550
Microchip Technology's PICmicro ® microcontrollers are popular because of
their low cost, wide availability, speed, capabilities, and low power con-
sumption. The PIC18F4550 is a PICmicro microcontroller with an embed-
ded USB device controller that can communicate at low and full speeds.
The chip doesn't have specific support for mass storage but is suitable for
mass-storage applications that need to store and transfer moderate quantities
of data at moderate speeds. The example firmware in this topic is written for
the PIC18F4550 and Microchip's C18 C compiler.
Architecture
The PIC18F4550 is a member of Microchip's high-performance, low-cost
PIC18 series. Program memory is flash memory. The chip also has 256
bytes of EEPROM. A bootloader routine can upgrade firmware via the USB
port.
The chip has 34 I/O pins that include a 10-bit analog-to-digital converter, a
USART, a synchronous serial port that can be configured to use the I 2 C bus
or SPI, enhanced PWM capabilities, and two analog comparators.
The USB module and CPU can use separate clock sources, enabling the
CPU to use a slower, power-saving clock even when using the USB port.
Firmware Support
Microchip provides USB Firmware Framework code for the Microchip
compiler and example applications for USB communications. The Frame-
work code is structured to make it as easy as possible to develop firmware for
devices in different classes and vendor-specific devices. This topic includes
excerpts from Microchip's mass-storage firmware, which uses the Frame-
work.
The USB Controller
The microcontroller's USB controller supports all four transfer types and up
to 30 endpoint addresses plus the default control endpoint. The endpoints