CY7C68310
Document 38-08030 Rev. *H
Page 13 of 34
6.1.1
I2C-compatible Device
The CY7C68310 provides support for the 24LCXXB family of
EEPROMs.
Following
the
release
of
nRESET,
the
CY7C68310 waits 50 ms and then checks for I2C-compatible
device presence. If an I2C-compatible device is present but
does not pass signature check, the CY7C68310 re-tests the
signature with each vendor-specific USB load or read access
of configuration bytes 0 and 1. Once the signature check
passes, I2C-compatible data is returned for USB descriptor
requests. If an I2C-compatible device is detected initially, it is
always assumed present until the next reset cycle (nRESET).
If an I2C-compatible device is present, a lack of an ACK
response when required causes the CY7C68310 to stall that
USB request. The CY7C68310 will attempt the access again
with the next USB request.
6.1.2
IMODE
Configuration and descriptor data can also be supplied by an
attached mass storage device (IMODE) through a vendor-
specific Identify (FBh) ATA command. The CY7C68310
provides 256 bytes of internal RAM for FBh data storage.
Unlike operation with an external I2C-compatible memory
device, IMODE operation requires the attached device first be
initialized and FBh data retrieved before the CY7C68310 can
allow USB enumeration. To meet USB specification require-
ments, IMODE operation must be limited to systems that draw
100 mA or less from VBUS prior to USB configuration.
6.1.3
Internal ROM Contents
The CY7C68310 also contains an internal set of CY7C68310
configuration and USB descriptors. The internal descriptors
may only be used during manufacturing, as the internal ROM
values disable some features required for normal operation to
aid use in a manufacturing environment. Also, the internal
ROM descriptors do not provide a unique serial number
(required for USB Mass Storage Class compliance), and
therefore cannot be used for shipping products. See Table 6-
2 for the organization of the internal ROM contents. An
external I2C-compatible memory device or utilization of the
vendor-specific FBh identify command is required to correctly
configure the CY7C68310 for operation and provide a unique
serial number for MSC compliance.
6.2
EEPROM Organization
CY7C68310 configuration and USB descriptor data can be
supplied from an I2C-compatible serial memory device. The
CY7C68310 can address 2 Kbytes of I2C-compatible data, but
CY7C68310 configuration and USB descriptor information are
limited to 512 bytes maximum. Unused register space in the
I2C-compatible serial memory device may be used for product
specific data storage. Note that no descriptor is allowed to
span multiple pages within the I2C-compatible serial memory
device.
Table 6-1. CY7C68310 Configuration and USB Descriptor Sources
SDA_nIMODE = 0
I2C-compatible
Device Present
I2C Signature
Check Passes CY7C68310 Configuration and USB Descriptor Retrieval Method
No
No
N/A
In this mode, the CY7C68310 uses internal ROM contents for USB
descriptor information and configuration register values. This mode is
for debug/manufacturing operation only. Not for shipping products.
Yes
N/A
No
In this mode, the CY7C68310 uses internal ROM contents for USB
descriptor information. Configuration register values are loaded from
internal ROM. This is not a valid mode of operation.
Yes
N/A
Yes
The CY7C68310 retrieves all Descriptor and Configuration values from
the vendor-specific Identify (FBh) data. The CY7C68310 is configured
using internal ROM values until FBh data becomes available.
No
Yes
No
The CY7C68310 uses internal ROM contents for USB descriptor infor-
mation. Configuration register values are loaded from internal ROM. In
this mode of operation, any CY7C68310 vendor-specific configuration
access causes the CY7C68310 to recheck the signature field. Once
the signature check passes, SROM data is returned for USB
descriptors requests. This is not a valid mode of operation.
No
Yes
Yes
The CY7C68310 retrieves all Descriptor and Configuration values from
the I2C-compatible memory device. The CY7C68310 is configured
using these values.
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