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EZ-USB Development Kit Manual - Getting Started

Page -8 EZ-USB Development Kit Manual - Getting Started Rev 1.0

“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 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

C transfer to address

1010000 (1010 is the EEPROM class address, and 000 is the sub-address). If the device supplies

an I

C acknowledge pulse, the EZ-USB loader writes a single EEPROM address byte to initialize

the internal EEPROM address pointer to zero.

If the above transfer does not return an ACK pulse, the EZ-USB loader initiates a second I

transfer, this time to address 10100001 (1010=EEPROM, sub-address 001). If an ACK is returned

by the I

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 ‘generic’ mode (explained

below).

Tree EZ-USB startup sequences, and the associated settings for SW1 and SW2, are shown

below.

1. Generic’: SW2=OFF, SW1=either position

When no EEPROM is connected to SCL and SDA, the EZ-USB chip enumerates using its

internal, “hard-wired” VID and PID values. This mode can be selected without requiring the

removal of any socketed EEPROMS by switching SW2 to the ‘off’ (down) position. This elec-

trically disconnects any EEPROMS that occupy the EEPROM sockets U5 and U6. The “OFF”

mode is handy for starting 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

debug tools. Once running, SW2 can be switched to the ON position to allow 8051 access, for

example to re-program the EEPROM.

2. ‘C0 Load’: SW2=ON, SW1=SMALL

A “C0” load provides EZ-USB with external VID, PID and DID values, allowing it to enumerate

with the EEPROM-supplied VID/PID/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 Vendor ID

(VID), Product ID (PID), Device ID (DID), and an EZ-USB configuration byte. Then when EZ-

USB enumerates, it uses these EEPROM values rather than the hard-wired internal values.

Since only eight bytes of data are required, a ‘small’ EEPROM is generally used for this mode,

for example the 16-byte 24LC00.

Table 2. Typical EZ-USB external EEPROMS

EEPROM Type Size A2A1A0 Typical P/N

“Small” 16x8 000 24LC00

128x8 000 24LC01

256x8 000 24LC02

“Large” 8Kx8 001 24LC64/5

1 2 ... 7 8 9 10 11 12 13 14 15 16 17 ... 27 28

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Cypress Semiconductor FX2LP Guide d'installation Page 12

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