MA31755 Datasheet, PDF (2/13 Pages) Dynex Semiconductor – 16-Bit Feedthrough Error Detection & Correction Unit EDAC

MA31755
1. PIN DESCRIPTIONS
POWER
VDD x8
VSS x8
Input -
Input -
Supply - 5V nominal (all must be connected)
Circuit 0V reference (all must be connected)
BUSSES
PD[0:16]
MD[0:16]
CB[0:5]
I/O
Active High
I/O
Active High
I/O
Active High
ERROR FLAGS AND CONTROL
CERRN
Output Active Low
NCERRN
Output Active Low
XERRN
ENCOR
Input
Input
Active Low
Active High
ENFLG
Input Active High
Processor data bus + parity bit (bit 16)
Memory data bus + parity bit (bit 16)
Memory check bit bus
Asserted low when a correctable (1 bit) error occurs (ENFLG
must be asserted high)
Asserted low when an uncorrectable error occurs (ENFLG
must be asserted high)
External error feedthrough to NCERRN line.
Enables correction of data when high. Data is passed
through uncorrected when this line is low.
Enables the flagging of incorrect data when high. When this
line is low the two error flag lines are held inactive.
DEVICE AND BUFFER CONTROL
CS2N
CS1N
CS0
RDWN
Input
Input
Input
Input
Active Low
Active Low
Active High
-
Enables device and output buffers.
Enables device and output buffers.
Enables device and output buffers.
High indicates a read cycle, low indicates a write cycle.
2. FUNCTIONAL DESCRIPTION
2.0 GENERAL
2.1 TESTING THE EDAC AND MEMORY SYSTEM
The EDAC is of feedthrough type with 16 data bits, 1 parity
bit and 6 check bits, giving the ability to correct all single bit
errors and detect all double bit errors. Errors in more than two
bits may result in any combination of error flags being raised
and the data may be arbitrarily modified by the correction
circuitry.
The EDAC is placed in the data bus between the processor
and the memory to be protected. It forms the interface
between the 23-bit memory bus and the 17-bit processor bus.
Tri-statable bus transceivers with a high drive capability are
incorporated at both busses.
No specific hardware for testing is provided by the
MA31755 since this would compromise the speed
performance of the part in normal operation. However, it is
possible to fully test the EDAC function and the generation of
the error signals without this. The system should provide a
means by which the check bit memory may be dynamically
write-enabled and disabled - this may be provided by gating
write strobe on the check bit memory with a latched control bit.
By writing first with check bits enabled, then with them
disabled, suitable seed values may be constructed which have
the required pattern of bits to test each feature of the EDAC
operation. A similar approach may be taken when testing the
check bit memory.
By disabling the EDAC (asserting ENCOR low) the
processor may have direct access to the unmodified 17-bit
data from the memory. Suitable test patterns may be applied to
test each memory location as required.
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