Cypress AN2131SC 제품 설명서 - 페이지 8

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Turbo Performance

The EZ-USB family

provides the maximum

performance specified for

USB. This allows the

peripheral manufacturer to

take advantage of USB's

full bandwidth in high-

speed applications such as

full-motion video,

continuous audio, scanning,

digital photography, and

printing.

EZ-USB Series 2100

To make full use of the USB

bandwidth, the EZ-USB family

has large endpoint buffers and a

fast method for transferring data

into and out of the buffers. With

the EZ-USB architecture, bulk

and isochronous endpoints can

be configured as double-buffered

with maximum packet sizes.

With the 2-Kbyte FIFO, the

EZ-USB family can transfer a

1024-byte isochronous packet

within a single USB frame.

Similarly for bulk endpoints, the

EZ-USB can transfer data using

the 64-byte double buffer capa-

bilities at a data transfer rate of

greater than 2 Mbytes per

second.

Fast transfer rates can occur in

and out of the internal FIFOs to

external peripherals since the

EZ-USB core automatically

monitors 8051 transfers between

the accumulator and the end-

point FIFO registers. When one of

these transfers occurs, the

EZ-USB core also reads or writes

the FIFO data over the external

data bus and provides external

FIFO read and write strobes for

the external interface.

Turbo Isochronous

Capability

The EZ-USB family provides

1024 bytes of double-buffered

FIFO memory (2048 bytes in all)

which may be divided between

16 isochronous endpoints.

During any one millisecond

frame time, one of the FIFOs is

connected to the USB and the

other to the 8051. At every SOF

(Start Of Frame), the buffers

"ping-pong" so the 8051 can

access the last frame's data while

the other FIFO empties or fills

with new USB data.

A single "movx" instruction

transfers data between EZ-USB

endpoint FIFOs and external logic

in two cycles or 330 nano seconds.

Based on these connections a

complete 1024-byte transfer can

take 388 microseconds, less than

40% of the 1 ms USB frame time.

This is an equivalent transfer rate

of greater than 2 Mbytes per

second.

Turbo Bulk Capability

USB bulk endpoint data is avail-

able to the 8051 as 16 64-byte

buffers in RAM. A special bulk

data pointer allows this RAM data

to also be accessed as a FIFO. The

8051 loads this sixteen-bit pointer

with the address of a bulk buffer.

Then, using a special data register,

accesses the buffer data as if it

were a FIFO. Every read or write

to the data register increments the

address pointer. This gives the

8051 a third data pointer: one that

auto-increments.

As with the fast isochronous

mode, the special data register

uses the turbo mode that allows a

byte of data to be transferred

using a single "movx" instruction.

Bulk transfers in and out of the

8051 therefore can be done with

the speed of the isochronous

transfers, one byte every two

cycles (330 nanoseconds). This

performance can generate well

over the maximum allowable bulk

packets within a USB frame.