DS1985

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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.