
Chapter 1. Introducing EZ-USB FX2 Page 1-11
1.12 EZ-USB FX2 Architecture
Figure 1-7. FX2 56-pin Package Simplified Block Diagram
The FX2 packs all the intelligence required by a USB peripheral interface into a compact inte-
grated circuit. As Figure 1-7 illustrates, an integrated USB transceiver connects to the USB bus
pins D+ and D-. A Serial Interface Engine (SIE) decodes and encodes the serial data and performs
error correction, bit stuffing, and the other signaling-level tasks required by USB. Ultimately, the
SIE transfers parallel data to and from the USB interface.
The FX2 SIE operates at Full Speed (12 Mbits/sec) and High Speed (480 Mbits/sec) rates. To
accommodate the increased bandwidth of USB 2.0, the FX2 endpoint FIFOs and slave FIFOs
(which interface to external logic or processors) are unified to eliminate internal data transfer times.
The CPU is an enhanced 8051 with fast execution time and added features. It uses internal RAM
for program and data storage.
The role of the CPU in a typical FX2-based USB peripheral is twofold:
• It implements the high-level USB protocol by servicing host requests over the control
endpoint (endpoint zero)
• It is available for general-purpose system use
The high-level USB protocol is not bandwidth-critical, so the FX2’s CPU is well-suited for handling
host requests over the control endpoint. However, the data rates offered by USB 2.0 are too high
for the CPU to process the USB data directly. For this reason, the CPU is not usually in the high-
bandwidth data path between endpoint FIFOs and the external interface. Instead,
the CPU simply
configures the interface, then “gets out of the way” while the unified FX2 FIFOs move the data
directly between the USB and the external interface.
Serial
Interface
Engine
(SIE)
USB
Transceiver
D+
D-
USB
Connector
OUT
data
IN
data
I/O Ports
USB
Interface
Slave
FIFOs
Program &
Data
RAM
EZ-USB FX2
GPIF
16
CPU
(Enhanced
8051)
CTL RDY
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