PIC18F4550ESOSQTP datasheet(166/430 Pages) MICROCHIP

166 / 430 page

PIC18F2455/2550/4455/4550

DS39632D-page 164

Preliminary

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

occurrence of a single-ended zero on the bus. When

the USB module is enabled, this bit should be moni-

tored 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 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.

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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