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EZ-USB Development Kit User Guide, Doc. # 001-66390 Rev. *D
21
Advanced Development Board
Table 3-2. Typical EZ-USB external EEPROMS
Small EEPROMs are typically used to supply custom VID and PID information, allowing the EZ-USB
to enumerate with a driver associated with your EZ-USB design.
Large EEPROMs are typically used to boot-load code into the internal EZ-USB RAM, and then start
up the 8051 to execute this internal code, which performs the enumeration.
The EZ-USB loader determines the EEPROM size by first initiating an I
2
C transfer to address
1010000 (1010 is the EEPROM-class address, and 000 is the sub-address). If the device supplies
an I
2
C acknowledge pulse, the EZ-USB loader writes a single EEPROM address byte to initialize the
internal EEPROM address pointer to zero.
If this transfer does not return an ACK pulse, the EZ-USB loader initiates a second I
2
C transfer, this
time to address 10100001 (1010 = EEPROM, sub-address 001). If an ACK is returned by the I
2
C
device, the EZ-USB loader writes two EEPROM address bytes to initialize the internal EEPROM
address pointer to 0.
If neither transfer returns an ACK pulse, the EZ-USB loader boots in the ‘generic’ mode.
Three EZ-USB startup sequences and the associated settings for SW1 and SW2, are as follows:
■
Generic: SW2 = No EEPROM, SW1 = either position
When no EEPROM is connected to SCL and SDA, the EZ-USB chip enumerates using its inter-
nal, “hard-wired” VID and PID values. This mode can be selected without removing any socketed
EEPROMs by switching SW2 to the ‘off’ (down) position. This electrically disconnects any
EEPROMs that occupy the EEPROM sockets U5 and U6. The “OFF” mode is useful to start up
EZ-USB in a manner (using internal VID/PID) that binds the development system board to the
Cypress debug tools, such as the Control Panel and Keil. When running, SW2 can be switched to
the ON position to allow 8051 access, for example, to reprogram the EEPROM.
■
C0 Load: SW2 = EEPROM, SW1 = SMALL
A “C0” load provides EZ-USB with external Vendor ID (VID), Product ID (PID), and Device ID
(DID) values, allowing it to enumerate with the EEPROM-supplied VID, PID, and DID. At power-
on, if the EZ-USB chip detects an EEPROM with the hex value ‘C0’ as its first byte, it continues to
load seven additional EEPROM bytes, which correspond to the USB VID, PID, DID, and an EZ-
USB configuration byte. When EZ-USB enumerates, it uses these EEPROM values instead of
the hard-wired internal values.
Because only eight bytes of data are required, a ‘small’ EEPROM is generally used for this mode;
for example, the 16-byte 24LC00.
■
C2 Load: SW2 = EEPROM, SW1 = LARGE
A “C2” load provides a method to load the EZ-USB internal RAM with 8051 firmware before enu-
meration. This boot load mechanism allows EZ-USB to enumerate as a fully custom device,
because the 8051 code handles enumeration using VID/PID values embedded in the code.
At power-on, if the EZ-USB chip detects an EEPROM with the hex value ‘C2’ as its first byte, it
continues to load an EZ-USB configuration byte, followed by blocks of 8051 code. The last byte
loaded takes the 8051 out of reset. This mode usually requires a large EEPROM, such as the
8 KB 24LC64.
EEPROM Type
Size
A2A1A0
Typical P/N
Small 16×8 000 24LC00
128×8 000 24LC01
256×8 000 24LC02
Large
8K×8 001
24LC64/5
Содержание CY3674
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