AD1821 Analog Devices, AD1821 Datasheet - Page 42

• Manufacturer Part Number: AD1821
• Manufacturer: Analog Devices

AD1821
PROGRAMMING EXTERNAL EEPROMS
The PnP EEPROM can be written only in the “Alternate Key State”; this prevents accidental EEPROM erasure when using stan-
dard PnP setup. The procedure for writing an EEPROM is:
1) Enter PnP configuration state and fully reset the part by writing 0x07 to PnP register 0x02. This step can be eliminated if the part
2) Send the alternate initiation key to the PnP address port. EEPROM writes are disabled if the standard PnP key is used.
3) Enter isolation state and write a CSN to enter configuration state. Do not perform any isolation reads.
4) Poll PnP register 0x05 until it equals 0x01 and wait at least 336 microseconds (ensures that EEPROM is idle).
5) Write the second byte of your serial identifier to PnP register 0x20.
6) Read PnP register 0x04.
7) Wait for at least 464 microseconds, plus the EEPROM’s write cycle time (up to 10 ms for a Xicor X24C02).
8) Repeat steps 4 through 7 for each byte in your PnP ROM, starting with the third byte of the serial identifier and ending with the
9) Fully reset the part by writing 0x07 to PnP register 0x02.
The AD1821 will now act according to the contents of the EEPROM.
NOTES
Programming will not work if more than one part uses the same alternate initiation key in the system.
If a 256-byte EEPROM is used, it is not necessary to wait 10 ms after writing bytes 255 to 511, because the EEPROM will ignore
them anyway.
You can skip over bytes that you don’t care to write by just performing a ROM read instead of a ROM write followed by a ROM read.
REFERENCE DESIGNS AND DEVICE DRIVERS
Reference designs and device drivers for the AD1821 are available via the Analog Devices Home Page on the World Wide Web at
http://www.analog.com. Reference designs may also be obtained by contacting your local Analog Devices Sales representative or
authorized distributor.
has not been accessed since power-up, a previous full PnP reset or assertion of the ISA bus RESET signal.
final checksum byte. You must then continue to write filler bytes until 512 bytes, minus one more than the number of flag bytes,
have been written. Finally, write the flag byte(s) (described above) and the first byte of the serial identifier.
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