Electrical computers and digital processing systems: support – Clock – pulse – or timing signal generation or analysis – Counting – scheduling – or event timing
Reexamination Certificate
2000-03-30
2003-06-03
Heckler, Thomas M. (Department: 2185)
Electrical computers and digital processing systems: support
Clock, pulse, or timing signal generation or analysis
Counting, scheduling, or event timing
Reexamination Certificate
active
06574743
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention relates to a programmable logic controller (PLC).
2. Related Information
Programmable logic controllers (PLC's) are a relatively recent development in process control technology. As a part of process control, a PLC is used to monitor input signals from a variety of input points (input sensors) which report events and conditions occurring in a controlled process. For example, a PLC can monitor such input conditions as motor speed, temperature, pressure, volumetric flow and the like. A control program is stored in a memory within the PLC to instruct the PLC what actions to take upon encountering particular input signals or conditions. In response to these input signals provided by input sensors, the PLC derives and generates output signals which are transmitted via PLC output points to various output devices, such as actuators and relays, to control the process. For example, the PLC issues output signals to speed up or slow down a conveyer, rotate the arm of a robot, open or close a relay, raise or lower temperature as well as many other possible control functions too numerous to list.
The input and output points referred to above are typically associated with input modules and output modules, respectively. Input modules and output modules are collectively referred to as I/O modules herein. Those skilled in the art alternatively refer to such I/O modules as I/O cards or I/O boards. These I/O modules are typically pluggable into respective slots located on a backplane board in the PLC. The slots are coupled together by a main bus which couples any I/O modules plugged into the slots to a central processing unit (CPU). The CPU itself can be located on a card which is pluggable into a dedicated slot on the backplane of the PLC.
FIG. 36
shows one typical conventional programmable logic controller system as system
3610
. System
10
includes a host programmable logic controller
3615
coupled by a field bus
3620
to a bus interface unit
3625
. Bus interface unit
3625
couples and interfaces field bus
3620
to a local bus
3630
which includes a plurality of I/O terminal blocks
3635
. I/O terminal blocks
3635
are coupled to respective I/O modules
3640
as shown in FIG.
1
.
In system
3610
, computational processing is performed by the host programmable logic controller
3615
. In other words conditions are sensed at I/O modules
3640
and input data is derived therefrom. The input data is transferred through bus interface unit
3625
and field bus
3620
to host programmable logic controller
3615
. Host programmable logic controller
3615
acts on the input data according to a control program stored in host PLC
3615
. Host programmable logic controller
3615
processes the input data and produces output data in response thereto. The output data is transferred through field bus
3620
, bus interface unit
3625
, local bus
3630
to one or more I/O modules
3640
. In response to the output data, the I/O module receiving the output data controls an output device coupled to the I/O module. I/O termination blocks are provided for coupling the I/O modules
3640
to the bus interface unit
3625
.
The PLC may be arranged in a master/slave network as shown in
FIG. 37
a
. In the figure, the master/slave control system includes a master PLC(M) and a plurality of remote slave units RSUs(R
1
-Rn). As shown therein, the master PLC(M) including a master PLC, a data link, and an I/O module, controls its own I/O connection points using a program and a communication parameter which are set by a user, and also controls the respective I/O connection points for the remote slave units R
1
-Rn. Each of the plurality of RSUs(R
1
-Rn) has at least one I/O module, and carries out a data communication with the master PLC(M) through a communication cable, and accordingly controls its own I/O module. The RSUs may be PLCs acting as slaves.
With reference to
FIG. 37
b
, the PLC and each of the RSUs include: a MODEM
3710
for carrying out a communication between the master PLC(M) and the RSUs via a communication cable; a receive/transmit module
3711
for exchanging data with the master PLC(M) according to a predetermined protocol; a receive/transmit buffer
3712
for temporarily storing therein the data for the exchange; an output data storage unit
3713
for storing therein the data which are to be transmitted from the master PLC(M) to an input/output module
3716
; an input data storage unit
3714
for storing therein the data which are to be transmitted from the input/output module
3716
to the master PLC(M); and an input/output control module
3715
for controlling a data transmission between the data storage units
3713
,
3714
and the input/output module
3716
.
In operation, the data link in the master PLC(M) is a data linking device attached to the master PLC(M), which operates as a master unit in the related network, and which obtains an initiative of the data communication. The data link is able to set a maximum number N of RSUs. The RSU sets each number of its own and the master PLC(M), and receives a communication directly from the master PLC(M) for thereby carrying out a data transmission. The data link in the master PLC(M) sequentially selects the RSUs(R
1
-Rn) and carries out a data receiving/transmitting operation. For example, when the data outputted from the master PLC(M) is applied through the communication cable and the MODEM
3710
to the RSU(R
1
), the applied data passes through the receive/transmit buffer
3712
and the receive/transmit module
3711
, and is stored in the output data storage unit
3713
. The data stored in the output data storage unit
3713
is outputted to the input/output module
3716
in accordance with the control of the input/output control module
3715
. The external control target data read from the input/output module
3716
of the remote slave unit R
1
is stored in the input data storage unit
3714
in accordance with the control of the input/output control module
3715
. The data stored in the input data storage unit
3714
is transmitted through the receive/transmit buffer
3712
and the receive/transmit module
3711
to the master PLC(M).
The present invention provides new features that enhance and extend the capability of the conventional PLC.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to enhance and extend the capability of the PLC.
It is another object of the invention to provide a digital input filter to enhance and extend the input capability of the PLC.
It is still another object of the invention to provide a pulse catch circuit to enhance and extend the pulse catching capability of the PLC.
It is yet another object of the invention to provide a pulse output controller to enhance and extend the output capability of the PLC.
It is a further an object of the invention to provide a free port link to enhance and extend the portability of the PLC.
It is still a further object of the invention to provide a protocol for modem communication to enhance and extend the connectivity of the PLC.
It is yet further an object of the invention to provide a hide instruction to enhance and extend the integration of the PLC with external programming applications.
It is still an additional object of the invention to provide a system function call to enhance and extend the function call capability of the PLC.
It is an additional object of the invention to provide an STL status to enhance and extend the status acquisition capability of the PLC.
It is yet and additional object of the invention to provide a micro PLC with an enhanced and extended capability.
In accordance with the foregoing objectives, the present invention provides a programmable logic controller with enhances and extended the capabilities.
In one aspect of the invention, a digital input filter is provided. The digital input filter simulates the action of a capacitor being driven by a constant current source whose output voltage is sensed by a comparator with a large amount of hysterisis. The digit
Boggs Mark Steven
Fulton Temple L.
Hausman Steve
McNabb Gary
McNutt Alan
Heckler Thomas M.
Siemens Energy & Automation
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