PIC18F2450_08 Datasheet, PDF (132/324 Pages) Microchip Technology – 28/40/44-Pin, High-Performance, 12 MIPS, Enhanced Flash, USB Microcontrollers with nanoWatt Technology

PIC18F2450/4450
14.2 USB Status and Control
The operation of the USB module is configured and
managed through three control registers. In addition, a
total of 22 registers are used to manage the actual USB
transactions. The registers are:
• USB Control register (UCON)
• USB Configuration register (UCFG)
• USB Transfer Status register (USTAT)
• USB Device Address register (UADDR)
• Frame Number registers (UFRMH:UFRML)
• Endpoint Enable registers 0 through 15 (UEPn)
14.2.1 USB CONTROL REGISTER (UCON)
The USB Control register (Register 14-1) contains bits
needed to control the module behavior during transfers.
The register contains bits that control the following:
• Main USB Peripheral Enable
• Ping-Pong Buffer Pointer Reset
• Control of the Suspend Mode
• Packet Transfer Disable
In addition, the USB Control register contains a status
bit, SE0 (UCON<5>), which is used to indicate the
occurrence of a single-ended zero on the bus. When
the USB module is enabled, this bit should be
monitored to determine whether the differential data
lines have come out of a single-ended zero condition.
This helps to differentiate the initial power-up state from
the USB Reset signal.
The overall operation of the USB module is controlled
by the USBEN bit (UCON<3>). Setting this bit activates
the module and resets all of the PPBI bits in the Buffer
Descriptor Table to ‘0’. This bit also activates the on-
chip voltage regulator, if enabled. Thus, this bit can be
used as a soft attach/detach to the USB. Although all
status and control bits are ignored when this bit is clear,
the module needs to be fully preconfigured prior to
setting this bit.
REGISTER 14-1: UCON: USB CONTROL REGISTER
U-0
—
bit 7
R/W-0
R-x
R/C-0
R/W-0
PPBRST
SE0
PKTDIS
USBEN
R/W-0
RESUME
R/W-0
SUSPND
U-0
—
bit 0
Legend:
R = Readable bit
-n = Value at POR
C = Clearable bit
W = Writable bit
‘1’ = Bit is set
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared
x = Bit is unknown
bit 7
Unimplemented: Read as ‘0’
bit 6
PPBRST: Ping-Pong Buffers Reset bit
1 = Reset all Ping-Pong Buffer Pointers to the EVEN Buffer Descriptor (BD) banks
0 = Ping-Pong Buffer Pointers not being reset
bit 5
SE0: Live Single-Ended Zero Flag bit
1 = Single-ended zero active on the USB bus
0 = No single-ended zero detected
bit 4
PKTDIS: Packet Transfer Disable bit
1 = SIE token and packet processing disabled, automatically set when a SETUP token is received
0 = SIE token and packet processing enabled
bit 3
USBEN: USB Module Enable bit
1 = USB module and supporting circuitry enabled (device attached)
0 = USB module and supporting circuitry disabled (device detached)
bit 2
RESUME: Resume Signaling Enable bit
1 = Resume signaling activated
0 = Resume signaling disabled
bit 1
SUSPND: Suspend USB bit
1 = USB module and supporting circuitry in Power Conserve mode, SIE clock inactive
0 = USB module and supporting circuitry in normal operation, SIE clock clocked at the configured rate
bit 0
Unimplemented: Read as ‘0’
DS39760D-page 130
© 2008 Microchip Technology Inc.