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THE CONTROL PORT
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The CONTROL PORT is a complete 8 bit Input/
Output Port used for internal and external
control functions. The operation of the Control
Port is easily understood if we separate its
functions into two categories: 1)Input Functions;
and 2) Output Functions.
CONTROL PORT INPUT FUNCTIONS
As an input port, the eight bits of the
Control Port serve to monitor 1) the status of
the CRI, S I O , and PIO ports; and 2) external
I/O control lines. All input functions of the
Control Port are determined by the configuration
of the INPUT JUMPER AREA (IJ A ) .
CONTROL PORT OUTPUT FUNCTIONS
As an output port, the eight bits of the
Control Port are used for external and internal
control functions according to the following
division.
1.
BITS 0-3
Bits 0-3 are latched and used to control
external devices when needed. The function
of these bits are determined by the config
uration of the OUTPUT JUMPER AREA (OJA).
2.
BITS 4-7
Bits 4-7 are latched and serve three func
tions: 1) to control CRI functions;
TABLE 3 shows the decoding of bits 4-7.
If either of the two status signals PIOS
or SIOS are used as an input to the Control
Port, bits 6 and 7 of the Control Port output
word are used to determine which of the error
2) to select PIO ports 1 or 2; and
3) to decode the status signals PIOS
and SIOS.
UbCi
UUJ.UB
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