STR720 datasheet(292/401 Pages) STMICROELECTRONICS

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STR720 - USB SLAVE INTERFACE (USB)

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Bit 15

CTR_RX: Correct Transfer for reception

This bit is set by the hardware when an OUT/SETUP transaction is

successfully completed on this endpoint; the software can only clear this bit. If

the CTRM bit in USB_CNTR register is set accordingly, a generic interrupt

condition is generated together with the endpoint related interrupt condition,

which is always activated. The type of occurred transaction, OUT or SETUP,

can be determined from the SETUP bit described below.

A transaction ended with a NAK or STALL handshake does not set this bit,

since no data is actually transferred, as in the case of protocol errors or data

toggle mismatches.

This bit is read/write but only ‘0’ can be written, writing 1 has no effect.

Bit 14

DTOG_RX: Data Toggle, for reception transfers

If the endpoint is not 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 having a matching data PID value; if the

endpoint is defined as a control one, hardware clears this bit at the reception

of a SETUP PID addressed to this endpoint.

If the endpoint is using the double-buffering feature this bit is used to support

packet buffer swapping too (Refer to Section “Double-Buffered Endpoints”).

If the endpoint is Isochronous, this bit is used only to support packet buffer

swapping since no data toggling is used for this sort of endpoints and only

DATA0 packet are transmitted (Refer to Section “Isochronous Transfers”).

Hardware toggles this bit just after the end of data packet reception, since no

handshake is used for isochronous transfers.

This bit can also be toggled by the software to initialize its value (mandatory

when the endpoint is not a control one) or to force specific data toggle/packet

buffer usage. When the application software writes ‘0’, the value of DTOG_RX

remains unchanged, while writing ‘1’ makes the bit value toggle. This bit is

read/write but it can be only toggled by writing 1.

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