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Organization
The Circuit Planes
Backplane Interface
Circuits
Midplane Circuits
Frontplane Circuits
To understand how the MUX card circuitry is organized, it is convenient
to think of the card as being divided into three planes of circuits. While
each plane would theoretically perform specific tasks, the planes actually
work in concert to accomplish some operations. The three major circuits
are:
•
Backplane interface circuits
•
Midplane circuits
•
Frontplane interface circuits
Figure 3-2 is a functional block diagram of the PCA circuitry. It shows
additional subdivisions, outlined with broken lines, within each plane. We
have also shown the card internal data bus. Data move in either direction
on the data bus to
all
of the circuit planes.
These circuits handle
all
data transfer, control, and handshaking lines be-
tween the card and the CIO backplane. The backplane interface as-
sembles data headed to the computer into the format used on the CIO
backplane. Data from the computer are decoded and routed to whatever
controller or data storage locations are dictated by the computer.
The midplane circuits manipulate data which come into the RAM from
either the backplane or the frontplane. By following programs in the
EPROM and the RAM, the Z-SO microprocessor controls the frontplane.
Based on those programs, the microprocessor rearranges data or inter-
prets it as commands.
The frontplane circuits convert the form of the data prepared by the
microprocessor to the form required by the communication protocols RS-
232-C and V.24. These circuits also do the reverse conversion on data
from the peripherals.
As Figure 3-2 indicates, in this plane, the data move on separate transmit
and receive lines. Each of the six channels for peripherals has individual
transmit and receive lines. Data on these lines move more slowly than
data on
the
interface internal data bus.
Functional Description 3-3
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