BQ2024 Datasheet, PDF (6/19 Pages) Texas Instruments – 1.5K-BIT SERIAL EPROM WITH SDQ INTERFACE

bq2024
SLUS770 – MAY 2007
www.ti.com
MATCH ROM
The MATCH ROM command, 55h, is used by the host to select a specific SDQ device when the family code and
identification number is known. The host issues the MATCH ROM command followed by the family code, ROM
number, and the CRC byte. Only the device that matches the 64-bit ROM sequence is selected and available to
perform subsequent Memory/Status Function commands.
Reset
and
Presence
Match ROM (55h)
Signals ^{1 0}
10
10
10
Family Code and Identification
Number (7 BYTES)
CRC (1 BYTE)
Figure 4. MATCH ROM Sequence
SEARCH ROM
The SEARCH ROM command, F0h, is used to obtain the 8-bit family code and the 48-bit identification number
and 8-bit CRC of any SDQ device when it is unknown. All devices on the bus are read under the SEARCH ROM
command with the use of a collision-detect and device-decode method. Figure 5 shows the SEARCH ROM
sequence started by the host, generating the RESET pulse of at least 480 µs. The bq2024 responds with a
PRESENCE pulse. The host then issues the command in the command frame by writing an F0h. During the
DATA READ of the SEARCH ROM sequence, each bit is transmitted three times. The bq2024 transmits the bit
followed by the complement of the bit. The host in turn retransmits the bit just read. Collision detection is
performed by comparing the bit and bit complement time-slots. If they are both zero, this indicates that a
collision has occurred, indicating multiple devices on the bus. The device decode is achieved in the third
transmission of the bit from the host back to the bq2024. If the bit transmitted by the host does not match the bit
transmitted by the bq2024, then the device with mismatch stops transmitting. Devices that did match, continue
transmitting. This process is continued until all bits of a single device are read. The SEARCH ROM command is
reissued and the process is repeated to read additional devices.
NOTE:
If the number of devices on the bus is unknown, the SEARCH ROM command should
be used.
Reset
and
Presence
Search ROM (F0h)
Signals ⁰
0
0
0
1
11
1
BIT0
Data Read
BITn
BIT63
A. B = bit(n): nth bit transmitted by bq2024
B. C = bit(n): complement of nth bit transmitted by bq2024
C. H = bit(n): nth bit transmitted by host
Figure 5. SEARCH ROM Sequence
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