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.
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.
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.
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
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.
