BQ2022_13 Datasheet, PDF (14/20 Pages) Texas Instruments – 1K-BIT SERIAL EPROM WITH SDQ INTERFACE

bq2022
SLUS526F – OCTOBER 2002 – REVISED DECEMBER 2006
www.ti.com
READ
The READ bit timing diagram in Figure 15 shows that the host initiates the transmission of the bit by issuing the
t_RSTRB portion of the bit. The bq2022 then responds by either driving the DATA bus low to transmit a READ 0 or
releasing the DATA bus to transmit a READ 1.
VPU _{V IH}
V _IL
Read ”1”
Read ”0”
t _RSTRB
t _ODD
t _ODHO
Figure 15. Read Bit Timing Diagram
t _REC
PROGRAM PULSE
V_PP
V_PU
V_SS
t_PSU
t_PRE
t_EPROG
t_PFE
t_PREC
Figure 16. Program Pulse Timing Diagram
IDLE
If the bus is high, the bus is in the IDLE state. Bus transactions can be suspended by leaving the DATA bus in
IDLE. Bus transactions can resume at any time from the IDLE state.
CRC Generation
The bq2022 has an 8-bit CRC stored in the most significant byte of the 64-bit ROM. The bus master can
compute a CRC value from the first 56 bits of the 64-bit ROM and compare it to the value stored within the
bq2022 to determine if the ROM data has been received error-free by the bus master. The equivalent polynomial
function of this CRC is: X⁸ + X⁵ + X⁴ +1.
Under certain conditions, the bq2022 also generates an 8-bit CRC value using the same polynomial function just
shown and provides this value to the bus master to validate the transfer of command, address, and data bytes
from the bus master to the bq2022. The bq2022 computes an 8-bit CRC for the command, address, and data
bytes received for the WRITE MEMORY and the WRITE STATUS commands and then outputs this value to the
bus master to confirm proper transfer. Similarly, the bq2022 computes an 8-bit CRC for the command and
address bytes received from the bus master for the READ MEMORY, READ STATUS, and READ DATA/
GENERATE 8-BIT CRC commands to confirm that these bytes have been received correctly. The CRC
generator on the bq2022 is also used to provide verification of error-free data transfer as each page of data from
the 1024-bit EPROM is sent to the bus master during a READ DATA/GENERATE 8-BIT CRC command, and for
the eight bytes of information in the status memory field.
In each case where a CRC is used for data transfer validation, the bus master must calculate a CRC value using
the polynomial function previously given and compare the calculated value to either the 8-bit CRC value stored
in the 64-bit ROM portion of the bq2022 (for ROM reads) or the 8-bit CRC value computed within the bq2022.
The comparison of CRC values and decision to continue with an operation are determined entirely by the bus
master. No circuitry on the bq2022 prevents a command sequence from proceeding if the CRC stored in or
calculated by the bq2022 does not match the value generated by the bus master. Proper use of the CRC can
result in a communication channel with a high level of integrity.
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