COMMUNICATION INTERFACE MODULE
WHICH IS CONFIGURABLE BY A
REMOVABLE MEMORY CARTRIDGE
BACKGROUND OF THE INVENTION
The present invention relates to programmable controllers which are employed to control the operation of one or more pieces of manufacturing equipment, and more particularly to 10 modules which interface the programmable controller to external devices using a serial communication link.
Programmable controllers, such as the one described in U.S. Pat. No. 4,858,101, typically are connected to industrial equipment, such as assembly lines and machine tools, to sequentially operate the equipment in accordance with a stored control program. The control program comprises instructions which are read out in rapid sequence and executed to examine the condition of selected sensing devices on the controlled equipment, or to energize or deenergize selected operating devices on the controlled equipment contingent upon the status of one or more of the examined sensing devices.
Many types of sensing devices have been devised for 25 detecting various conditions on the controlled equipment and providing an input signal to the programmable controller. The simplest of these types of devices are switches which provide a DC or an AC signal to the programmable controller. Other devices, such as temperature or pressure 3Q sensors provide a four to twenty milliampere signal having a magnitude which corresponds to the magnitude of the condition being sensed. Similarly with respect to the operating devices, the programmable controller must be capable of providing a variety of electrical output signals either DC, 35 AC or analog current signals for driving the different types of operating devices on the controlled equipment. In order to provide a programmable controller capable of being interfaced to a wide variety of industrial equipment, modularized controllers have been developed which allow the use of 4Q different combinations of input and output modules depending upon the requirements of the specific industrial equipment being controlled.
As industrial processes became more complex, a more sophisticated sensing and control system was required. In 45 many instances, the simple voltage or current inputs and outputs of the programmable controller were insufficient to communicate the data to and from the equipment. In many instances, more sophisticated sensors were devised to provide detailed data about the individual workpieces being 50 handled by the controlled equipment. For example, automobile assembly lines use radio frequency transponder tags mounted either on the automobile or the assembly line carriage for the automobile. As the automobile passes a work station, a transceiver mounted on the work station interro- 55 gates the RF transponder tag to acquire data about the specific automobile being processed. Such data, for example, identifies the model of car as well as the options and features to be incorporated. Once the transceiver has interrogated the transponder tag, the data regarding the go automobile is provided to a programmable controller at the work station over a serial communication link.
Various types of these sophisticated sensing and operating devices, manufactured by different companies and utilizing different communication protocols may have to be inter- 65 faced to the same programmable controller. Although these devices often use standard public-domain serial communi
cation protocols, their manufacturers have also utilized proprietary protocols. In order to provide a programmable controller with the greatest degree of flexibility to connect a wide variety of sensing and operating devices, the programmable controller must be configurable to communicate using of a variety of serial protocols. In addition, a given programmable controller in a specific installation may have to communicate using a number of different protocols simultaneously.
A large assembly line may be controlled by a number of programmable controllers. In which case, a serial communication network interconnects the programmable controllers allowing them to exchange data regarding the operation of the assembly line. A host computer is often coupled to the network to receive assembly line status information from the programmable controllers and issue commands to them.
SUMMARY OF THE INVENTION
A module provides a serial communication interface for coupling input and output (I/O) devices and other remote apparatus to a programmable controller. The module contains a serial port circuit which has a processor that executes a program to supervise the exchange data between the programmable controller and the external devices. The exchange of data utilizes a defined serial communication protocol and the processor can execute different programs depending upon which protocol is being used. The port circuit also includes a memory for storing the program executed by the processor. In addition, signal drivers are provided to electrically couple the module to a communication link for the external devices.
The communication module further includes a connector into which a removable memory cartridge may be inserted. The memory cartridge provides non-volatile storage for a program that controls the processor. A mechanism is provided in the module to transfer the program from the memory cartridge to the memory in the port circuit. This enables the communication protocol to be changed by changing the memory cartridge and transferring a different program into the port circuit memory.
In the preferred embodiment, the commumcation module has a number of port circuits so that several serial communication links may be coupled to the module. Although this embodiment has particular applicability as a input module for a programmable controller, it may also be used in a stand-alone manner interconnecting the serial commumcation links for the exchange of data among the links. The same or different programs may be executed by each port circuit processor, thereby enabling communication with different protocols. In this case, several programs are stored in one memory cartridge or multiple memory cartridge connectors are provided. Configuration data is stored in the module indicating from which memory cartridge the program for each port circuit is to be transferred.
A communication protocol used by the communication module can require the user to select parameter options, such as baud rate, the length of the data characters, and the number of stop bits. The user is afforded the opportunity to configure the port circuit by selecting specific options. However, different protocols can have different parameters, which means that the port circuit configuration procedure is dependent upon the particular protocol being used. Therefore, a set of protocol parameter inquiries is stored in the memory cartridge along with the protocol program. These inquiries are transferred into the communication module and