1.13.1 EZ-USB Bulk Endpoints
Bulk endpoints are unidirectional—one endpoint address per direction. Therefore end-
point 2-IN is addressed differently than endpoint 2-OUT. Bulk endpoints use maximum
packet sizes (and therefore buffer sizes) of 8, 16, 32, or 64 bytes. EZ-USB provides four-
teen bulk endpoints, divided into seven IN endpoints (endpoint 1-IN through 7-IN), and
seven OUT endpoints (endpoint 1-OUT through 7-OUT). Each of the fourteen endpoints
has a 64-byte buffer.
Bulk data is available to the 8051 in RAM form, or as FIFO data using a special EZ-USB
Autopointer (Chapter 6, "EZ-USB Bulk Transfers").
1.13.2 EZ-USB Control Endpoint Zero
Control endpoints transfer mission-critical control information to and from the USB
device. The Universal Serial Bus Specification Version 1.1 requires every USB device to
have a default CONTROL endpoint, endpoint zero. Device enumeration, the process that
the host initiates when the device is first plugged in, is conducted over endpoint zero. The
host sends all USB requests over endpoint zero.
Control endpoints are bi-directional; if you have an endpoint 0 IN CONTROL endpoint,
you automatically have an endpoint 0 OUT endpoint. Control endpoints alone accept
SETUP PIDs.
A CONTROL transfer consists of a two or three stage sequence:
•
•
•
SETUP
DATA (If needed)
HANDSHAKE
Eight bytes of data in the SETUP portion of the CONTROL transfer have special USB
significance, as defined in the Universal Serial Bus Specification Version 1.1, “Chapter
9.” A USB device must respond properly to the requests described in this chapter to pass
USB compliance testing (usually referred to as the USB “Chapter Nine Test”).
Endpoint zero is the only CONTROL endpoint in the EZ-USB chip. The 8051 responds to
device requests issued by the host over endpoint zero. The EZ-USB core is significantly
enhanced to simplify the 8051 code required to service these requests. Chapter 7, "EZ-
USB Endpoint Zero" provides a detailed roadmap for writing USB Chapter 9 compliant
8051 code.
EZ-USB TRM v1.9
Chapter 1. Introducing EZ-USB
Page 1-13
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