ST7SCR1R4T1 datasheet(49/102 Pages) STMICROELECTRONICS

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ST7SCR

49/102

USB INTERFACE (Cont’d)

ENDPOINT 0 REGISTER (EP0R)

Read/Write

Reset value: 0000 0000(00h)

This register is used for controlling Endpoint 0.

Bits 6:4 and bits 2:0 are also reset by a USB reset,

either received from the USB or forced through the

FRES bit in USBCTLR.

Bit 7 = CTR0

Correct Transfer.

This bit is set by hardware when a correct transfer

operation is performed on Endpoint 0. This bit

must be cleared after the corresponding interrupt

has been serviced.

0: No CTR on Endpoint 0

1: Correct transfer on Endpoint 0

Bit 6 = DTOG_TX

Data Toggle, for transmission

transfers.

It contains the required value of the toggle bit

(0=DATA0, 1=DATA1) for the next transmitted

data packet. This bit is set by hardware on recep-

tion of a SETUP PID. DTOG_TX toggles only

when the transmitter has received the ACK signal

from

the

USB

host.

DTOG_TX

and

also

DTOG_RX are normally updated by hardware, on

receipt of a relevant PID. They can be also written

by the user, both for testing purposes and to force

a specific (DATA0 or DATA1) token.

Bits 5:4 = STAT_TX [1:0]

Status bits, for transmis-

sion transfers.

These bits contain the information about the end-

point status, which are listed below

Table 15. Transmission Status Encoding

These bits are written by software. Hardware sets

the STAT_TX and STAT_RX bits to NAK when a

correct transfer has occurred (CTR=1) addressed

to this endpoint; this allows software to prepare the

next set of data to be transmitted.

Bit 3 = Reserved, forced by hardware to 0.

Bit 2 = DTOG_RX

Data Toggle, for reception

transfers.

It contains the expected value of the toggle bit

(0=DATA0, 1=DATA1) for the next data packet.

This bit is cleared by hardware in the first stage

(Setup Stage) of a control transfer (SETUP trans-

actions start always with DATA0 PID). The receiv-

er toggles DTOG_RX only if it receives a correct

data packet and the packet’s data PID matches

the receiver sequence bit.

CTR0

DTOG

_TX

STAT_

TX1

STAT_

TX0

DTOG

_RX

STAT_

RX1

STAT_

RX0

STAT_TX1 STAT_TX0

Meaning

DISABLED: no function can be

executed on this endpoint and

messages related to this end-

point are ignored.

STALL: the endpoint is stalled

and all transmission requests

result in a STALL handshake.

NAK: the endpoint is NAKed

and all transmission requests

result in a NAK handshake.

VALID: this endpoint is enabled

(if an address match occurs, the

USB interface handles the

transaction).

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