The Other Half of the I2C Story
The EZ-USB I2C controller serves two purposes. First, as described in this chapter, it
manages the serial EEPROM interface that operates automatically at power-on to deter-
mine the enumeration method. Second, once the 8051 is up and running, the 8051 can
access the I2C controller for general-purpose use. This makes a wide range of standard
I2C peripherals available to an EZ-USB system.
Other I2C devices can be attached to the SCL and SDA lines of the I2C bus as long as
there is no address conflict with the serial EEPROM described in this chapter. Chapter 4,
"EZ-USB Input/Output" describes the general-purpose nature of the I2C interface.
5.6
No Serial EEPROM
In the simplest case, no serial EEPROM is present on the I2C bus, or an EEPROM is
present but its first byte is not 0xB0 or 0xB2. In this case, descriptor data is supplied by a
table internal to the EZ-USB core. The EZ-USB chip comes on as the USB Default
Device, with the ID bytes shown in Table 5-6.
Table 5-6. EZ-USB Device Characteristics, No Serial EEPROM
0x0547 (Cypress Semiconductor)
0x2131 (EZ-USB)
Vendor ID
Product ID
0xXXYY (depends on revision)
Device Release
The USB host queries the device during enumeration, reads the device descriptor, and uses
the Table 5-6 bytes to determine which software driver to load into the operating system.
This is a major USB feature—drivers are dynamically matched with devices and automat-
ically loaded when a device is plugged in.
The no_EEPROM case is the simplest configuration, but also the most limiting. This
mode is used only for code development, utilizing Cypress software tools matched to the
ID values in Table 5-6.
Page 5-8
Chapter 5. EZ-USB CPU
EZ-USB TRM v1.9
CYPRESS [ CYPRESS ]
