DS1982

Page 11 of 24

READ MEMORY [F0h]

The Read Memory command is used to read data from the 1024-bit EPROM 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. An 8–bit CRC of the command byte and address bytes is computed by

the DS1982 and read back by the bus master to confirm that the correct command word and starting

address were received. If the CRC read by the bus master is incorrect, a Reset Pulse must be issued and

the entire sequence must be repeated. If the CRC received by the bus master is correct, the bus master

issues read time slots and receives data from the DS1982 starting at the initial address and continuing

until the end of the 1024-bit data field is reached or until a Reset Pulse is issued. If reading occurs

through the end of memory space, the bus master may issue eight additional read time slots and the

DS1982 will respond with an 8-bit CRC of all data bytes read from the initial starting byte through the

last byte of memory. After the CRC is received by the bus master, any subsequent read time slots will

appear as logical 1s until a Reset Pulse is issued. Any reads ended by a Reset Pulse prior to reaching the

end of memory will not have the 8-bit CRC available.

Typically a 16-bit CRC would be stored with each page of data to ensure rapid, error-free data transfers

that eliminate having to read a page multiple times to determine if the received data is correct or not. (See

Book of DS19xx iButton Standards, Chapter 7 for the recommended file structure to be used with the

1-Wire environment.) If CRC values are imbedded within the data, a Reset Pulse may be issued at the end

of memory space during a Read Memory command.

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 two-byte address (TA1=(T7:T0), TA2=(T15:T8)) that indicates a

starting byte location within the data field. An 8–bit CRC of the command byte and address bytes is

computed by the DS1982 and read back by the bus master to confirm that the correct command word and

starting address were received. If the CRC read by the bus master is incorrect, a Reset Pulse must be

issued and the entire sequence must be repeated. If the CRC received by the bus master is correct, the bus

master issues read time slots and receives data from the DS1982 starting at the supplied address and

continuing until the end of the EPROM Status data field is reached. At that point the bus master will

receive an 8-bit CRC that is the result of shifting into the CRC generator all of the data bytes from the

initial starting byte through the final factory-programmed byte that contains the 00h value.

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 an 8-bit CRC that is based on and always is consistent with the current

data stored in the EPROM Status data field.

After the 8-bit CRC is read, the bus master will receive logical 1s from the DS1982 until a Reset Pulse is

issued. The Read Status command sequence can be exited at any point by issuing a Reset Pulse.

READ DATA/GENERATE 8-BIT CRC [C3h]

The Read Data/Generate 8-bit CRC command is used to read data from the 1024-bit EPROM memory

field. The bus master follows the command byte with a two-byte address (TA1=(T7:T0), TA2=(T15:T8))

that indicates a starting byte location within the data field. An 8-bit CRC of the command byte and

address bytes is computed by the DS1982 and read back by the bus master to confirm that the correct

command word and starting address were received. If the CRC read by the bus master is incorrect, a

Reset Pulse must be issued and the entire sequence must be repeated. If the CRC received by the bus

master is correct, the bus master issues read time slots and receives data from the DS1982 starting at the