The 8051 communicates with the SIE using a set of registers, which occupy the top of the
on-chip RAM address space. These registers are grouped and described by function in
individual chapters of this reference manual, and summarized in register order in Chapter
12, "EZ-USB Registers."
The EZ-USB 8051 has two duties. First, it participates in the protocol defined in the Uni-
versal Serial Bus Specification Version 1.1, “Chapter 9, USB Device Framework.”
Thanks to EZ-USB enhancements to the SIE and USB interface, the 8051 firmware asso-
ciated with USB overhead is simplified, leaving code space and bandwidth available for
the 8051’s primary duty, to help implement your device. On the device side, abundant
input/output resources are available, including IO ports, UARTs, and an I2C bus master
controller. These resources are described in Chapter 4, "EZ-USB Input/Output."
1.12 ReNumeration
Because it is soft, the EZ-USB chip can take on the identities of multiple distinct USB
devices. The first device downloads your 8051 firmware and USB descriptor tables over
the USB cable when the peripheral device is plugged in. Once downloaded, another
device comes on as a totally different USB peripheral as defined by the downloaded infor-
mation. This two-step process, called ReNumeration , happens instantly when the
device is plugged in, with no hint that the initial load step has occurred.
Chapter 5, "EZ-USB Enumeration and ReNumeration‘" describes this feature in detail,
along with other EZ-USB boot (startup) modes.
1.13 EZ-USB Endpoints
The Universal Serial Bus Specification Version 1.1 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/fills with USB bytes. The host selects a device endpoint by sending a 4-bit
address and one direction bit. Therefore, USB can uniquely address 32 endpoints, IN0
through IN15 and OUT0 through OUT15.
From the EZ-USB point of view, an endpoint is a buffer full of bytes received or to be
transmitted over the bus. The 8051 reads endpoint data from an OUT buffer, and writes
endpoint data for transmission over USB to an IN buffer.
Four USB endpoint types are defined as: Bulk, Control, Interrupt, and Isochronous.
Page 1-12
Chapter 1. Introducing EZ-USB
EZ-USB TRM v1.9
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