ST92163 datasheet(145/224 Pages) STMICROELECTRONICS

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ST92163 - USB PERIPHERAL (USB)

USB INTERFACE (Cont’d)

ENDPOINT n REGISTER B (EPnRB)

(RECEPTION)

R241-R255 (odd) - Read/Write

Reset value: 0000 0000 (00h)

These registers are used for controlling data re-

ception. They are also reset when a USB reset is

received from the USB bus or forced through bit

FRES in the USBCTLR register. Each endpoint

has its EPnRB register where n is the endpoint

identifier in the range 0 to 15.

Bit 7 = ST_OUT

Status out.

This bit is set by software to indicate that a status

out transaction is expected: in this case all OUT

transactions containing more than zero data bytes

are answered STALL instead of ACK. This bit may

be used to improve the robustness of the applica-

tion to protocol errors during control transfers and

its usage is intended on control endpoints only.

When ST_OUT is reset, OUT transactions can

have any number of bytes, as needed.

Bit 6 = DTOG_RX:

Data Toggle, for reception

transfers.

If the endpoint is non-isochronous, this bit contains

the expected value of the data toggle bit

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

be received. Hardware toggles this bit when the

ACK handshake is sent to the USB host, following

a data packet reception with a matching data PID

value. If the endpoint is defined as a control end-

point, hardware resets this bit on reception of a

SETUP PID addressed to this endpoint.

If the endpoint is isochronous, this bit is used to

support DMA buffer swapping since no data tog-

gling is used for this sort of endpoint and only

DATA0 packets are received. Hardware toggles

this bit just after the end of data packet reception,

since no handshake is used for isochronous trans-

fers.

Note: this bit can be also written by software to in-

itialize it (mandatory when the endpoint is not a

control endpoint) or to force a specific data toggle/

DMA buffer usage.

Bit 5:4 = STAT_RX [1:0]

Status bits, for reception

transfers.

These bits contain the information about the end-

point status, as listed below:

Table 28. Reception status encoding

These bits are written by software, but hardware

sets the STAT_RX bits to NAK when a correct

transfer has occurred (CTR=1) related to a OUT or

SETUP (control only) transaction addressed to

this endpoint, so software has time to interpret the

received data before acknowledging a new trans-

action.

If the endpoint is defined as isochronous, its status

can be only “VALID” or “DISABLED” so no hard-

ware change of the endpoint status will take place

after a successful transaction.

Bit 3:0 = EnA[3:0]

Endpoint n Address, bits 3-0.

Software must write in this field the 4-bit address

used to identify the transactions directed to this

endpoint. A value must be written before enabling

the corresponding endpoint.

ST_OU

DTOG_

STA T_

RX1

STAT_

RX0

EnA3

EnA2

EnA1

EnA0

STAT_TX

[1:0]

Meaning

DISABLED: all reception requests ad-

dressed to this endpoint are ignored.

STALL: the endpoint is stalled and all re-

ception requests result in a STALL hand-

shake.

NAK: the endpoint is naked and all recep-

tion requests result in a NAK handshake.

VALID: this endpoint is enabled for recep-

tion.

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