UPSD3422 datasheet(152/293 Pages) STMICROELECTRONICS

152 / 293 page

USB interface

uPSD34xx

152/293

Figure 55.

FIFO pairing example (1/2 IN paired and 3/4 OUT paired)

25.3.4

Reading and writing FIFOs

There are a total of ten 64-byte FIFOs. Each of the five Endpoints has two FIFOs, one IN

FIFO for IN transactions and one OUT FIFO for OUT transactions. The FIFOs are

accessible by the CPU through a 64-byte segment in the XDATA space when the VISIBLE

Bit is set (see Table 80 on page 163). If the VISIBLE Bit is not set, the FIFOs are not

accessible by the CPU but are still accessible by the SIE. The base address of the 64-byte

segment is specified by the USB Base Address High Register (see Table 85 on page 168)

and the USB Base Address Low Register (see Table 86 on page 168). When the VISIBLE

Bit is set, the FIFO that is accessible in the 64-byte XDATA space segment is the FIFO

selected by the USEL register. The USEL register contains two fields used for selecting the

accessible FIFO. The EP field determines the Endpoint selected and the DIR Bit selects the

IN or OUT FIFO associated with the Endpoint.

25.3.5

Accessing FIFO control registers, UCON, and USIZE

Each of the 10 Endpoint FIFOs has an associated USB Endpoint Control Register (UCON,

0F1H) and a USB FIFO Valid Size Register (USIZE, 0F2H). The USB Endpoint Select

XDATA space, but also selects the associated Endpoint’s UCON and USIZE registers that

are accessible at SFR addresses 0F1H and 0F2H.

25.3.6

Accessing the setup command buffer

Setup Packets are sent from the host to a device’s Endpoint0 and consist of 8 bytes of

command data. When the SIE receives a Setup packet from the host, it stores the 8 bytes of

data in the Command Buffer. The command buffer is accessed via the indexed USB Setup

8032

MCU

USB SFRs

Serial

Interface

Engine

CTRL

XDATA

AI10494

Endpoint4 IN FIFO

Endpoint3 IN FIFO

Endpoint2 IN FIFO

Endpoint1 IN FIFO

Endpoint0 IN FIFO

Endpoint0 OUT FIFO

Endpoint1 OUT FIFO

Endpoint2 OUT FIFO

FIFO

Interface

Logic

Endpoint4

Endpoint3

Endpoint2

(not available)

Endpoint2

(not available)

Endpoint1

Endpoint0

Endpoint4

Endpoint3

Endpoint1

Endpoint0

Endpoint1

Endpoint2

Endpoint3

Endpoint0

Endpoint1

Endpoint2

Endpoint3

Endpoint4

(not available)

Endpoint4

(not available)

Endpoint3 OUT FIFO

Endpoint4 OUT FIFO

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