PIC16C55A-04/SP【PDF 38/194 页】IC MCU OTP 512X12 28DIP

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PIC18F2450/4450

DS39760A-page 130

Advance Information

2006 Microchip Technology Inc.

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

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

= Reset all Ping-Pong Buffer Pointers to the Even Buffer Descriptor (BD) banks

= Ping-Pong Buffer Pointers not being reset

bit 5

SE0: Live Single-Ended Zero Flag bit

= Single-ended zero active on the USB bus

= No single-ended zero detected

bit 4

PKTDIS: Packet Transfer Disable bit

= SIE token and packet processing disabled, automatically set when a SETUP token is received

= SIE token and packet processing enabled

bit 3

USBEN: USB Module Enable bit

= USB module and supporting circuitry enabled (device attached)

= USB module and supporting circuitry disabled (device detached)

bit 2

RESUME: Resume Signaling Enable bit

= Resume signaling activated

= Resume signaling disabled

bit 1

SUSPND: Suspend USB bit

= USB module and supporting circuitry in Power Conserve mode, SIE clock inactive

= 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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