PIC18F-LF1XK50 Datasheet, PDF (258/420 Pages) Microchip Technology – 20-Pin USB Flash Microcontrollers

PIC18F/LF1XK50
22.2.5 USB ADDRESS REGISTER
(UADDR)
The USB Address register contains the unique USB
address that the peripheral will decode when active.
UADDR is reset to 00h when a USB Reset is received,
indicated by URSTIF, or when a Reset is received from
the microcontroller. The USB address must be written
by the microcontroller during the USB setup phase
(enumeration) as part of the Microchip USB firmware
support.
22.2.6 USB FRAME NUMBER REGISTERS
(UFRMH:UFRML)
The Frame Number registers contain the 11-bit frame
number. The low-order byte is contained in UFRML,
while the three high-order bits are contained in
UFRMH. The register pair is updated with the current
frame number whenever a SOF token is received. For
the microcontroller, these registers are read-only. The
Frame Number registers are primarily used for
isochronous transfers. The contents of the UFRMH and
UFRML registers are only valid when the 48 MHz SIE
clock is active (i.e., contents are inaccurate when
SUSPND (UCON<1>) bit = 1).
22.3 USB RAM
USB data moves between the microcontroller core and
the SIE through a memory space known as the USB
RAM. This is a special dual access memory that is
mapped into the normal data memory space in Bank 2
(200h to 2FFh) for a total of 256 bytes (Figure 22-4).
Bank 2 (200h through 27Fh) is used specifically for
endpoint buffer control. Depending on the type of buff-
ering being used, all but 8 bytes of Bank 2 may also be
available for use as USB buffer space.
Although USB RAM is available to the microcontroller
as data memory, the sections that are being accessed
by the SIE should not be accessed by the
microcontroller. A semaphore mechanism is used to
determine the access to a particular buffer at any given
time. This is discussed in Section 22.4.1.1 “Buffer
Ownership”.
FIGURE 22-4:
IMPLEMENTATION OF
USB RAM IN DATA
MEMORY SPACE
000h
Banks 0
to 1
Banks 2
(USB RAM)
User Data
Buffer Descriptors,
USB Data or User Data
USB Data or
User Data
1FFh
200h
27Fh
280h
2FFh
300h
Banks 3
to 14
Unused
Banks 15
SFRs
F52h
F53h
F5Fh
F60h
FFFh
DS41350E-page 258
Preliminary
 2010 Microchip Technology Inc.