STR720 datasheet(269/401 Pages) STMICROELECTRONICS

269 / 401 page

STR720 - USB SLAVE INTERFACE (USB)

269/401

boundary (the lowest three bits of USB_BTABLE register are always “000”). Buffer descriptor

table entries are described in the Section “Buffer Descriptor Table”. If an endpoint is

unidirectional and it is neither an Isochronous nor a double-buffered bulk, only one packet

buffer is required (the one related to the supported transfer direction). Other table locations

related to unsupported transfer directions or unused endpoints, are available to the user.

isochronous and double-buffered bulk endpoints have special handling of packet buffers

(Refer to “Isochronous Transfers” and “Double-Buffered Endpoints” respectively). The

relationship between buffer description table entries and packet buffer areas is depicted in

Figure 41.

Figure 41. Packet Buffer Areas and Buffer Description Table Locations

ADDR0_TX

COUNT0_TX

0000_0000 (00)

ADDR0_RX

COUNT0_RX

ADDR1_TX

COUNT1_TX

ADDR1_RX

COUNT1_RX

ADDR2_TX

COUNT2_TX

ADDR2_RX

COUNT2_RX

ADDR3_TX

COUNT3_TX

0000_0010 (02)

0000_0100 (04)

0000_0110 (06)

0000_1000 (08)

0000_1010 (0A)

0000_1100 (0C)

0000_1110 (0E)

0001_0000 (10)

0001_0010 (12)

0001_0100 (14)

0001_0110 (16)

0001_1000 (18)

0001_1010 (1A)

Buffer description table locations

Transmission

buffer for

Endpoint 0

Reception buffer

for

Endpoint 0

Transmission

buffer for

Endpoint 1

Packet buffers

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