More Endpoint Buffer Memory
The EZ-USB chip supports more endpoints and provides more endpoint buffer memory than any other USB-device solution in the market. The USB specification describes an endpoint as a source or sink of data. In the EZ-USB chip, endpoints are constructed as RAM (bulk, control, interrupt endpoints) or FIFOs (isochronous endpoints). With support for 31 endpoints (the maximum in the USB specification), it gives the peripheral designer ultimate flexibility. Unlike other USB peripheral alternatives, the EZ-USB architecture also sup- ports the maximum packet size for each endpoint. Thus 64-byte packets are available for all control, bulk, and interrupt endpoints. Isochronous endpoints are double buffered with a packet size of up to 1024 bytes, the maximum allowable under the USB specification.
Control
The EZ-USB family supports one control endpoint. To simplify firmware programming, the EZ-USB chip provides data from
control transfers in two separate buffers. It also has a unique capability to manage the three- phase transfer in hardware, relieving device firmware from this task.
Bulk/Interrupt
Bulk endpoints are used when data integrity must be guaran- teed, but without critical delivery time. The EZ-USB family provides 14 bulk endpoints: seven IN and seven OUT. These endpoints can be programmed to be double- buffered, which improves trans- fer bandwidth in some applica- tions. Bulk data is accessible as RAM or FIFO data. The IN and OUT endpoints can also be used as interrupt endpoints.
Isochronous
These endpoints support stream- ing data such as audio or video. The EZ-USB family supports 16 isochronous endpoints: eight IN and eight OUT. A pool of FIFOs can be allocated among the endpoint to a maximum of
1 Kbyte. Isochronous endpoints are double-buffered, as required by the USB specification, so the actual size of iscochronous buffer memory is 2 Kbytes.
Low Power—Even for Bus-Powered Devices
The EZ-USB family meets the tough power specifications of USB. Running off of a 3.3V power supply, it can accommodate bus- powered devices and self-pow- ered peripherals. In addition, with a 50 mA current draw under full operating conditions, the EZ-USB family provides current headroom for peripheral func- tions. This meets the USB require- ment of 100 mA maximum current for attached peripherals prior to configuration. Total maximum power required by an EZ-USB chip under active condi- tions is 170 mW. Other solutions require five times more power.
