EZ-USB Datasheet, PDF (82/334 Pages) Cypress Semiconductor – The EZ-USB USB Integrated Circuit

5.5 Enumeration Modes
When the EZ-USB chip comes out of reset, the EZ-USB core makes a decision about how
to enumerate based on the contents of an external EEPROM on its I²C bus. Table 5-5
shows the choices. In Table 5-5, PID means Product ID, VID means Version ID, and DID
means Device ID.
Table 5-5. EZ-USB Core Action at Power-Up
First EEPROM byte
EZ-USB Core Action
Not 0xB0 or 0xB2
Supplies descriptors, PID/VID/DID from EZ-USB
Core. Sets ReNum=0.
0xB0
Supplies descriptors from EZ-USB core, PID/VID/DID
from EEPROM. Sets ReNum=0.
0xB2
Loads EEPROM into EZ-USB RAM. Sets ReNum=1;
therefore 8051 supplies descriptors, PID/VID/DID.
If no EEPROM is present, or if one is present but the first byte is neither 0xB0 nor 0xB2,
the EZ-USB core enumerates using internally stored descriptor data, which contains the
Cypress Semiconductor VID, PID, and DID. These ID bytes cause the host operating sys-
tem to load a Cypress Semiconductor device driver. The EZ-USB core also establishes the
Default USB device. This mode is only used for code development and debug.
If a serial EEPROM is attached to the I²C bus and its first byte is 0xB0, the EZ-USB core
enumerates with the same internally stored descriptor data as for the no-EEPROM case,
but with one difference. It supplies the PID/VID/DID data from six bytes in the external
EEPROM rather than from the EZ-USB core. The custom VID/PID/DID in the EEPROM
causes the host operating system to load a device driver that is matched to the EEPROM
VID/PID/DID. This EZ-USB operating mode provides a soft USB device using ReNu-
meration™.
If a serial EEPROM is attached to the I²C bus and its first byte is 0xB2, the EZ-USB core
transfers the contents of the EEPROM into internal RAM. The EZ-USB core also sets the
ReNum bit to 1 to indicate that the 8051 (and not the EZ-USB core) responds to device
requests over CONTROL endpoint zero (see the text box, “When ReNum=1 at Power-
On” on page 5-6). Therefore, all descriptor data, including VID/DID/PID values, are sup-
plied by the 8051 firmware. The last byte loaded from the EEPROM (to the CPUCS reg-
ister) releases the 8051 reset signal, allowing the EZ-USB chip to come up as a fully
custom device with firmware in RAM.
The following sections discuss these enumeration methods in detail.
EZ-USB TRM v1.9
Chapter 5. EZ-USB CPU
Page 5-7