DS1985-F3+ Maxim Integrated Products, DS1985-F3+ Datasheet - Page 8

• Manufacturer Part Number: DS1985-F3+
• Description: IBUTTON 16KBit ADD-ONLY F3
• Manufacturer: Maxim Integrated Products
• Series: iButton®r

Specifications of DS1985-F3+

• Rohs Information: IButton RoHS Compliance Plan
• Memory Size: 2KB
• Memory Type: EPROM
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

DS1985
READ STATUS [AAH]
The Read Status command is used to read data from the EPROM Status data field. The bus master
follows the command byte with a 2-byte address (TA1=(T7:T0), TA2=(T15:T8)) that indicates a starting
byte location within the data field. With every subsequent read data time slot the bus master receives data
from the DS1985 starting at the supplied address and continuing until the end of an 8-byte page of the
EPROM Status data field is reached. At that point the bus master will receive a 16-bit CRC of the
command byte, address bytes and status data bytes. This CRC is computed by the DS1985 and read back
by the bus master to check if the command word, starting address and data were received correctly. If the
CRC read by the bus master is incorrect, a Reset Pulse must be issued and the entire sequence must be
repeated.
Note that the initial pass through the Read Status flow chart will generate a 16-bit CRC value that is the
result of clearing the CRC generator and then shifting in the command byte followed by the two address
bytes, and finally the data bytes beginning at the first addressed memory location and continuing through
to the last byte of the addressed EPROM Status data page. The last byte of a Status data page always has
an ending address of xx7 or xxFH. Subsequent passes through the Read Status flow chart will generate a
16-bit CRC that is the result of clearing the CRC generator and then shifting in the new data bytes starting
at the first byte of the next page of the EPROM Status data field.
This feature is provided since the EPROM Status information may change over time making it impossible
to program the data once and include an accompanying CRC that will always be valid. Therefore, the
Read Status command supplies a 16-bit CRC that is based on and always is consistent with the current
data stored in the EPROM Status data field.
After the 16-bit CRC of the last EPROM Status data page is read, the bus master will receive logical 1s
from the DS1985 until a Reset Pulse is issued. The Read Status command sequence can be ended at any
point by issuing a Reset Pulse.
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