Memory Expansion Options; Operating Characteristics - IBM 5150 Hardware Reference Manual

Memory Expansion Options
Two Memory Expansion Options offered for the IBM Personal
Computer are the 32K x 9 and the 64K x 9 Memory Expansion
Options. These options plug into any ofthe five System Expansion slots
on the System Board. These options are used to extend system memory
beyond 64KB. A maximum of 64KB of memory may be installed on
the System Board as modules without using any System Expansion
Slots or Expansion Options.
An expansion option must be configured to reside at sequential32K or
64K memory address boundary within the system address space. This
is done by setting dip switches on the option.
The expansion options are designed with 250 ns access 16K x 1
dynamic memory chips. On the 32KB card, 16-pin industry standard
parts are used. On the 64 KB card, stacked modules are used resulting
in a 32K xI 18-pin module. This allows the 32KB and 64KB to have
approximately the same packaging densities.
Both expansion options are parity checked and if a parity error is
detected, a latch is set and an I/O channel check line is activated,
indicating an error to the processor.
".-,., In addition to the memory modules, the expansion options contain the
following circuits: bus buffering, dynamic memory timing generation,
address multiplexing, and card select decode logic.
Dynamic memory refresh timing and address generation are functions
which are not performed on the expansion options but are done once on
the System Board and made available in the I/O channel for all devices.
To allow the System to address 32KB and 64KB Memory Expansion
Options, refer to the system configuration switch settings page 2-28.
Operating Characteristics
The System Board operates at a frequency of 4.77 Mhz, which results
in a clock frequency of 210 ns.
Normally, four clock cycles are required for a bus cycle so that an
840 nsec memory cycle time is achieved. Memory write and memory
".-,., read cycles both take four clock cycles, or 840 ns.
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