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to the destination before the "end-of-message" is received.
If
a line is not immediately available,
the message is placed in queue storage to be transmitted in queue sequence.
The same basic process occurs for the character and word buffers.
BLOCK DIAGRAM
The simplified block diagram shows the main paths for the flow of data. Data is moved over each
path on an 18 bit parallel bus logic arrangement. For some instructions, data will be moved over
several paths, with data flowing on only one path at a time. An example of this is transferring
data from the B register to memory. The contents of B go to the Y register, straight through the
arithmetic unit to the Z drivers, and then to memory.
PFF
ZFF
EFF
Z DRIVERS
,.
l
I
REGISTERS, COUNTERS, SWITCHES : BUFFER UNITS
ARITHMETIC UNIT
I
l~
~
,,
MEMORY
LOWER DATA BUS
-
--
Y REGISTER
Figure 34. Simplified Block Diagram
Other instructions, however, can cause data to flow over "parallel" paths at the same time. For
example, performing the logical operation of combining the contents of the B register with a
word in memory and storing the result in the B register will result in the following: The contents
of the B register go to the Y register and on to the arithmetic unit. At the same time, the con-
tents of the memory location go to the arithmetic unit. The logical operation is performed on the
two words, the result goes to Z drivers; and is then placed in the B register in accordance with
the program.
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-46-
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