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PIC18F2455/2550/4455/4550

DS39632E-page 166

2009 Microchip Technology Inc.

17.2

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)

17.2.1

USB CONTROL REGISTER (UCON)

The USB Control register (Register 17-1) 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 occur-

rence of a single-ended zero on the bus. When the USB

module is enabled, this bit should be monitored to deter-

mine 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 the VREGEN Configuration bit is

set) and connects internal pull-up resistors, if they are

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.

Note:

When disabling the USB module, make

sure the SUSPND bit (UCON<1>) is clear

prior to clearing the USBEN bit. Clearing

the USBEN bit when the module is in the

suspended state may prevent the module

from fully powering down.

REGISTER 17-1:

UCON: USB CONTROL REGISTER

U-0

R/W-0

R-x

R/C-0

R/W-0

U-0

—

PPBRST

SE0

PKTDIS

USBEN

RESUME

SUSPND

—

bit 7

bit 0

Legend:

C = Clearable bit

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

-n = Value at POR

‘1’ = Bit is set

‘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’

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