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DP8402A Datasheet(PDF) 6 Page - National Semiconductor (TI)

[Old version datasheet] Texas Instruments acquired National semiconductor.
Part No. DP8402A
Description  DP8402A/DP8403/DP8404/DP8405 32-Bit Parallel Error Detection and Correction Circuits (EDACs)
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Manufacturer  NSC [National Semiconductor (TI)]
Direct Link  http://www.national.com
Logo NSC - National Semiconductor (TI)

DP8402A Datasheet(HTML) 6 Page - National Semiconductor (TI)

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TABLE VI Read-Modify-Write Function
DB OUTPUT
MEMORY
EDAC FUNCTION
CONTROL
BYTEn
OEBn
LATCH
CHECK IO
CB
ERROR FLAG
CYCLE
S1
S0
LEDBO
CONTROL
ERR MERR
Read
Read
Flag
H
L
Input
H
X
Input
H
Enabled
Input
Input
Read
Latch input data
H
H
data
H
L
check word
H
Enabled
check bits
latched
latched
Latch corrected
Output
Hi-Z
H
Read
data word into
H
H
data
HH
Output
Enabled
output latch
word
Syndrome
L
latched
bits
Input
Modify appropriate
modified
H
Modify
byte or bytes
LL
BYTE0
H
Output
LH
H
write
generate new
Ouput
check word
check word
unchanged
L
BYTE0
OEB0 controls DB0–DB7 (BYTE0) OEB1 controls DB8–DB15 (BYTE1) OEB2 controls DB16–DB23 (BYTE2) OEB3 controls DB24–DB31 (BYTE3)
Read-Modify-Write (Byte Control)
Operations
The DP8402A and DP8403 devices are capable of byte-
write operations The 39-bit word from memory must first be
latched into the DB and CB input latches This is easily ac-
complished by switching from the read and flag mode (S1 e
H SO e L) to the latch input mode (S1 e H S0 e H) The
EDAC will then make any corrections if necessary to the
data word and place it at the input of the output data latch
This data word must then be latched into the output data
latch by taking LEDBO from a low to a high
Byte control can now be employed on the data word
through the OEB0 through OEB3 controls OEB0 controls
DB0 – DB7 (byte 0) OEB1 controls DB8 – DB15 (byte 1)
OEB2 controls DB16 – DB23 (byte 2) and OEB3 controls
DB24 – DB31 (byte 3) Placing a high on the byte control will
disable the output and the user can modify the byte If a low
is placed on the byte control then the original byte is al-
lowed to pass onto the data bus unchanged If the original
data word is altered through byte control a new check word
must be generated before it is written back into memory
This is easily accomplished by taking control S1 and S0 low
Table VI lists the read-modify-write functions
Diagnostic Operations
The DP8402A thru DP8405 are capable of diagnostics that
allow the user to determine whether the EDAC or the mem-
ory is failing The diagnostic function tables will help the
user to see the possibilities for diagnostic control
In the diagnostic mode (S1 e L S0 e H) the checkword is
latched into the input latch while the data input remains
transparent This lets the user apply various data words
against a fixed known checkword If the user applies a diag-
nostic data word with an error in any bit location the ERR
flag should be low If a diagnostic data word with two errors
in any bit location is applied the MERR flag should be low
After the checkword is latched into the input latch it can be
verified by taking OECB low This outputs the latched
checkword With the DP8402A and DP8403 the diagnostic
data word can be latched into the output data latch and
verified It should be noted that the DP8404 and DP8405 do
not have this pass-through capability because they do not
contain an output data latch By changing from the diagnos-
tic mode (S1 e L S0 e H) to the correction mode (S1 e H
S0 e H) the user can verify that the EDAC will correct the
diagnostic data word Also the syndrome bits can be pro-
duced to verify that the EDAC pinpoints the error location
Table VII DP8402A and DP8403 and Table VIII DP8404 and
DP8405 list the diagnostic functions
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