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14 System architecture
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The system memory stores all operating software programs and data
unique to the particular Meridian 1 system, including switching
sequences, features, class of service information, and quantity and types
of terminals.
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The Mass Storage Unit provides high speed loading of the operating
programs and data into memory.
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The Digital Service Circuits provide functions such as dial and ringing
tones, and call conferencing capabilities.
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The Serial Data Interface (SDI) provides a RS232C communications
link for administration and maintenance on either a local or remote
basis.
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The Network Circuit Cards provide a digital matrix for circuit-switched
connections to associated peripheral devices.
Central Processing Unit (CPU)
The CPU performs the control and switching sequences required by the
system. The software that directs these functions is loaded into the system
memory from the mass storage unit by the CPU.
Information flows
between the CPU, I/O devices, and the system memory over the CPU bus.
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The data required by the CPU to perform its control and switching functions
is held during system operation in Random Access Memory (RAM) and fed
to the CPU via the CPU bus. The operating data is loaded into the RAM
from floppy diskettes on system power-up.
The CPU function is performed by circuit cards which include Read-Only-
Memory fiiware that contains fault clearing programs and instructions to
control the loading of system memory from the mass storage unit.
Meridian 1 systems incorporate a CPU design that is identical for most
system options.
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24-bit data words plus l-bit parity
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24-bit linear addressing that permits memory allocation to be assigned
on a contiguous basis instead of the 64K pages partitioning referenced
above
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16M words
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subdivided for up to 12M words of physical memory
space and a remainder of 4M words for I/O spaces
System overview 553-3001-100