Memory Expansion Cards; Parity And Refresh - HP Vectra Reference Manual

SECTION 10. MEMORY
EXPANSION
CARDS
For rnemory capabilities beyond 640 Kbyte, HP provides two
memory expansion cards: the HP45973A 1/2 MB Memory
Expansion Card which contains 512 Kbytes of RAM, and the
HP45974A 1 MB Memory Expansion Card which supports 1024
Kbytes of RAM.
The memory expansion cards use 256K x 1 dynamic memory
chips. The HP45973A 1/2 MB Memory Expansion Card contains
18 of these RAM chips (including parity). The HP45974A 1 MB
Memory Expansion Card contains 36 of these chips.
The memory expansion cards, must be inserted into two
connector 16-bit I/O slots. Table 2.4 and table 2.5 give the pin
assignments for these connectors, and signal descriptions can be
found in Section 2.
Parity and Refresh
Memory data is parity-checked when accessed. If a parity error
occurs, then a non-maskable interrupt (NMl) will be generated.
The NMI can be cleared by writing to the memory expansion card
where the parity error occurred.
Refresh of dynamic memory is controlled on the main system
card. All memories using the -- REFRESH line are refreshed at the
same time.
Memory Expansion Cards 115