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DP8402AV Datasheet(PDF) 6 Page - National Semiconductor (TI) |
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DP8402AV Datasheet(HTML) 6 Page - National Semiconductor (TI) |
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6 / 18 page  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 6 |
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