Apple Lisa - Memory Errors

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Lisa Hardware Reference Manual
MEMORY ERRORS
Two kinds of memory error can be detected during a memory access,
Hard Error and Soft Error. A Hard Error is a parity error during a
parity memory board access or an uncorrectable error during an ECC
memory board access. A Soft Error indicates that a correctable error
has been detected on an ECC memory board access. If either the Hard
Error (HDER) or Soft Error (SFER) Signal is asserted at the end of a
memory cycle, a latch on the CPU board latches the address at Which
the error occurred, and asserts the NMI signal Which interrupts the
68000. The address latches latch the high order 16 bits (segment
num~er and page number) of the address. The cause of the error is
latched in the system status register. A program can therefore log
soft errors in ECC boards and keep track of hard failures in main
memory on a page by page baSiS, and the MMU can be used to map out
bad pages.
Detection of either 'hard or soft memory errors can be disabled. Each
error type has an Enable Memory Error Detect Bit. If the bit is set,
errors are detected and latched. If the bit is reset, error
detection is masked. At power on, both kinds of memory error
detection are masked off. To set soft error detection, read or write
to the address $00E016 in I/O space. To reset soft error detection,
read or write to $00E014. Hard error detection is enabled by a read
or write to $OOE01E, and disabled by a read or write to $OOE01C.
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7-Jul-81