ST7261 datasheet(38/80 Pages) STMICROELECTRONICS

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ST7261

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USB INTERFACE (Cont’d)

PID REGISTER (PIDR)

Read only

Reset Value: xx00 0000 (x0h)

Bits 7:6 = TP[3:2]

Token PID bits 3 & 2.

USB token PIDs are encoded in four bits. TP[3:2]

correspond to the variable token PID bits 3 & 2.

Note: PID bits 1 & 0 have a fixed value of 01.

When a CTR interrupt occurs (see register ISTR)

the software should read the TP3 and TP2 bits to

retrieve the PID name of the token received.

The USB standard defines TP bits as:

Bits 5:3 Reserved. Forced by hardware to 0.

Bit 2 = RX_SEZ

Received single-ended zero

This bit indicates the status of the RX_SEZ trans-

ceiver output.

0: No SE0 (single-ended zero) state

1: USB lines are in SE0 (single-ended zero) state

Bit 1 = RXD

Received data

0: No K-state

1: USB lines are in K-state

This bit indicates the status of the RXD transceiver

output (differential receiver output).

Note: If the environment is noisy, the RX_SEZ and

RXD bits can be used to secure the application. By

interpreting the status, software can distinguish a

valid End Suspend event from a spurious wake-up

due to noise on the external USB line. A valid End

Suspend is followed by a Resume or Reset se-

quence. A Resume is indicated by RXD=1, a Re-

set is indicated by RX_SEZ=1.

Bit 0 = Reserved. Forced by hardware to 0.

INTERRUPT STATUS REGISTER (ISTR)

Read / Write

Reset Value: 0000 0000 (00h)

When an interrupt occurs these bits are set by

hardware. Software must read them to determine

the interrupt type and clear them after servicing.

Note: These bits cannot be set by software.

Bit 7 = SUSP

Suspend mode request.

This bit is set by hardware when a constant idle

state is present on the bus line for more than 3 ms,

indicating a suspend mode request from the USB

bus. The suspend request check is active immedi-

ately after each USB reset event and its disabled

by hardware when suspend mode is forced

(FSUSP bit of CTLR register) until the end of

resume sequence.

Bit 6 = DOVR

DMA over/underrun.

This bit is set by hardware if the ST7 processor

can’t answer a DMA request in time.

0: No over/underrun detected

1: Over/underrun detected

Bit 5 = CTR

Correct Transfer. This bit is set by

hardware when a correct transfer operation is per-

formed. The type of transfer can be determined by

looking at bits TP3-TP2 in register PIDR. The End-

point on which the transfer was made is identified

by bits EP1-EP0 in register IDR.

0: No Correct Transfer detected

1: Correct Transfer detected

Note: A transfer where the device sent a NAK or

STALL handshake is considered not correct (the

host only sends ACK handshakes). A transfer is

considered correct if there are no errors in the PID

and CRC fields, if the DATA0/DATA1 PID is sent

as expected, if there were no data overruns, bit

stuffing or framing errors.

Bit 4 = ERR

Error.

This bit is set by hardware whenever one of the er-

rors listed below has occurred:

0: No error detected

1: Timeout, CRC, bit stuffing or nonstandard

framing error detected

TP3

TP2

000

RX_

SEZ

RXD

TP3

TP2

PID Name

OUT

SETUP

SUSP

DOVR

CTR

ERR

IOVR

ESUSP

RESET

SOF

ST7261 数据表(PDF) 38 Page - STMicroelectronics

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