+5V
Program &
Data
RAM
D+
D-
bytes
bytes
Serial
Interface
Engine
(SIE)
USB
Interface
IO Ports
GND
External
Address Bus
Data Bus
General
Purpose
Microprocessor
Memory,
FIFOS,
etc.
USB
Connector
USB
Transceiver
EZ-USB
Figure 1-2. AN2131Q (80 pin) Simplified Block Diagram
Figure 1-2 illustrates the An2131Q, an 80-pin version of the EZ-USB family. In addition
to the 24 IO pins, it contains a 16-bit address bus and an 8-bit data bus for external mem-
ory expansion.
A special fast transfer mode moves data directly between external logic and internal USB
FIFOs. The fast transfer mode, along with abundant endpoint resources, allows the EZ-
USB family to support transfer bandwidths beyond the maximum required by the Univer-
sal Serial Bus Specification Version 1.1.
1.3
The USB Specification
The Universal Serial Bus Specification Version 1.1 is available on the Internet at http://
usb.org. Published in January 1998, the specification is the work of a founding commit-
tee of seven industry heavyweights: Compaq, DEC, IBM, Intel, Microsoft, NEC, and
Northern Telecom. This impressive list of implementers secures USB as the low to
medium speed PC connection method of the future.
A glance at the USB Specification makes it immediately apparent that USB is not nearly
as simple as the customary serial or parallel port. The specification uses new terms like
“endpoint,” isochronous,” and “enumeration,” and finds new uses for old terms like “con-
figuration,” “interface,” and “interrupt.” Woven into the USB fabric is a software abstrac-
tion model that deals with things such as “pipes.” The specification also contains detail
about the connector types and wire colors.
EZ-USB TRM v1.9
Chapter 1. Introducing EZ-USB
Page 1-3
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