Cypress Semiconductor FX2LP Informacje Techniczne Pobierz pdf (Strona 49)

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Chapter 1. Introducing EZ-USB FX2 Page 1-23

1.18 FX2 Endpoint Buffers

The USB Specification defines an endpoint as a source or sink of data. Since USB is a serial bus,

a device endpoint is actually a FIFO which sequentially empties or fills with USB data bytes. The

host selects a device endpoint by sending a 4-bit address and a direction bit. Therefore, USB can

uniquely address 32 endpoints, IN0 through IN15 and OUT0 through OUT15.

From the FX2’s point of view, an endpoint is a buffer full of bytes received or held for transmission

over the bus. The FX2 reads host data from an OUT endpoint buffer, and writes data for transmis-

sion to the host to an IN endpoint buffer.

FX2 contains three 64-byte endpoint buffers, plus 4 Kilobytes of buffer space that can be config-

ured various ways, as indicated by Figure 1-15. The three 64-byte buffers are common to all con-

figurations.

Figure 1-15. FX2 Endpoint Buffers

The three 64-byte buffers are designated EP0, EP1IN and EP1OUT. EP0 is the default CONTROL

endpoint, a bidirectional endpoint that uses a single 64-byte buffer for both IN and OUT data. FX2

firmware reads or fills the EP0 buffer when the (optional) data stage of a CONTROL transfer is

required.

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