One of the most important features of the EZ-USB family is that it is soft. Instead of
requiring ROM or other fixed memory, it contains internal program/data RAM that is
downloaded over the USB itself to give the device its unique personality. This make mod-
ifications, specification revisions, and updates a snap.
The EZ-USB family can connect as a USB device and download code into internal RAM,
all while its internal 8051 is held in RESET. This is done by an enhanced SIE, which does
all of the work shown in Figure 1-8, and more. It contains additional logic to perform a
full enumeration, using an internal table of descriptors. It also responds to a vendor spe-
cific “Firmware Download” device request to load its internal RAM. An added bonus is
that the added SIE functionality is also made available to the 8051. This saves 8051 code
and processing time.
Throughout this manual, the SIE and its enhancements are referred to as the “USB Core.”
1.11 EZ-USB Microprocessor
The EZ-USB microprocessor is an enhanced 8051 core. Use of an 8051 compatible pro-
cessor makes extensive software support tools immediately available to the EZ-USB
designer. This enhanced 8051 core, described in Chapter 2, "EZ-USB CPU" and Appen-
dices A-C, has the following features:
•
4-clock cycle, as compared to the 12-clock cycle of a standard 8051, giving a 3X
speed improvement.
•
•
•
•
•
•
•
Dual data pointers for faster memory-to-memory transfers.
Two UARTs.
Three counter-timers.
An expanded interrupt system.
24-MHz clock.
256 bytes of internal register RAM.
Standard 8051 instruction set—if you know the 8051, you know EZ-USB
The enhanced 8051 core uses on-chip RAM as program and data memory, giving EZ-USB
its soft feature. Chapter 3, "EZ-USB Memory" describes the various memory options.
EZ-USB TRM v1.9
Chapter 1. Introducing EZ-USB
Page 1-11
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