TNETX15AE Datasheet, PDF (15/78 Pages) Texas Instruments – ADDRESS-LOOKUP DEVICE

TNETX15AE
ADDRESS-LOOKUP DEVICE
SPWS041A – AUGUST 1997 – REVISED OCTOBER 1997
EEPROM auto-configuration from an external x24C02 EEPROM (continued)
The organization of the EEPROM data is shown in Table 4. The last register loaded is the control register. This
allows a complete initialization by downloading the contents of the EEPROM into the TNETX15AE. During the
download, no DIO operations are permitted. The LOAD and RESET bits in the control register cannot be set
during a download, preventing a download loop.
The TNETX15AE has reserved space in the register map with corresponding reserved space in the EEPROM.
This is to support additional features in future revisions of the device with minimal impact on software drivers
written for this device. Although the TNETX15AE does not use the values in the reserved EEPROM locations
to load the reserved locations in the register map, the auto-loader reads every address from the beginning of
the EEPROM to the CRC to calculate the CRC. That is, changing a loaded value or a reserved value requires
a new CRC for the EEPROM.
The TNETX15AE detects the presence/absence of the EEPROM. If it is not installed, the EDIO terminal should
be tied low. For EEPROM operation, the terminal requires an external pullup (see EEPROM data sheet). When
no EEPROM is detected, the TNETX15AE assumes default register values at power up and is halted.
Downloading a configuration from the EEPROM terminals is disabled when no EEPROM is present.
The first bit written to or read from the EEPROM is the most-significant bit of the byte, i.e., data (7). Therefore,
writing the address 0xC0 is accomplished by writing a 1 and then 1, 0, 0, 0, 0, 0, 0. For details of reading, writing,
or programming a 24C02 device, refer to the device data sheet.
The TNETX15AE causes data to be stored in the EEPROM in a specific format. The range from 0x00 to 0x2A
in the EEPROM is reserved for use by the adapter. The contents of the remaining bytes are undefined. The
EEPROM can be read/written by driver software through the SIO register.
A 32-bit CRC value must be calculated from the EEPROM data and placed in the EEPROM in the location
following the bytes loaded into the internal registers. The TNETX15AE uses this 32-bit CRC to validate the
EEPROM data. If the CRC fails, the TNETX15AE registers are set to their default (hardwired) values. This is
the same state the TNETX15AE is in if no EEPROM is present. Without an EEPROM, a management CPU is
required to load all the registers and set the start bit to 1 in the upper one-half of the control/status register (0x08).
The CRC calculation on the EEPROM bytes is the same as the IEEE Std 802.3u for the packet CRC calculation
on a byte-by-byte basis. For reference, the equation is:
+ ) ) ) ) ) ) ) ) ) ) ) ) ) ) G(x) x³² x²⁶ x²³ x²² x¹⁶ x¹² x¹¹ x¹⁰ x⁸ x⁷ x⁵ x⁴ x² x 1
(1)
The TNETX15AE EEPROM register assignments are shown in Table 4.
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