ST72774 datasheet(83/144 Pages) STMICROELECTRONICS

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ST72774/ST727754/ST72734

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USB INTERFACE (Cont’d)

ENDPOINT n REGISTER A (EPnRA)

Read / Write

Reset Value: 0000 xxxx (0xh)

These registers (EP0RA, EP1RA and EP2RA) are

used for controlling data transmission. They are

also reset by the USB bus reset.

Note: Endpoint 2 and the EP2RA register are not availa-

ble on some devices (see device feature list and

Bit 7 = ST_OUT

Status out.

This bit is set by software to indicate that a status

out packet is expected: in this case, all nonzero

OUT data transfers on the endpoint are STALLed

instead of being ACKed. When ST_OUT is reset,

OUT transactions can have any number of bytes,

as needed.

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 at the

reception 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 (see EPnRB) are normally updated by

hardware, at the receipt of a relevant PID. They

can be also written by software.

Bits

5:4

STAT_TX[1:0]

Status

bits,

for

transmission transfers.

These bits contain the information about the

endpoint status, which are listed below:

These bits are written by software. Hardware sets

the STAT_TX bits to NAK when a correct transfer

has occurred (CTR=1) related to a IN or SETUP

transaction addressed to this endpoint; this allows

the software to prepare the next set of data to be

transmitted.

Bits 3:0 = TBC[3:0]

Transmit byte count for

Endpoint n.

Before transmission, after filling the transmit

buffer, software must write in the TBC field the

transmit packet size expressed in bytes (in the

range 0-8).

ST_

OUT

DTOG

_TX

STAT

_TX1

STAT

_TX0

TBC

STAT_TX1 STAT_TX0 Meaning

DISABLED: transmission

transfers cannot be execut-

ed.

STALL: the endpoint is

stalled and all transmission

requests result in a STALL

handshake.

NAK: the endpoint is naked

and all transmission re-

quests result in a NAK hand-

shake.

VALID: this endpoint is ena-

bled for transmission.

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