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Section 2: Functional Overview
CCM Operation
MegaBasic Operation
For CCM applications, each port behaves like an independent window into the PLC for
access by other devices using the CCM protocol, such as industrial computers and color
graphic terminals. The implementation of CCM on the PCM supports access to most
user references. Many applications which accessed Series Six user references using CCM
can now support the Series 90 PLC with little or no change.
Either port of the PCM can be configured in CCM MASTER, SLAVE, or PEER mode. In
this capacity, the PCM acts much like a Series Six CCM module, transfering data between
the PLC and an external device. Configuration of the port parameters is done in the
Logicmaster 90 configuration package, using CCM mode. In SLAVE or PEER mode, an
external CCM device, such as a computer, can request and send PLC CPU data to the
PCM’s ports. In MASTER or PEER mode, the application program in the PLC CPU can
use the COMMREQ instruction to initiate data transfers to a CCM device attached to a
PCM port.
As a programmable coprocessor, the PCM may be programmed with a powerful BASIC
language interpreter called MegaBasic to perform data acquisition, data storage and
retrieval, real-time computing, and operator interface functions. GE Fanuc has added
extensions to MegaBasic to permit the reading and writing of user references in the PLC.
These extensions also access program and system status information, permitting the
development of operator interface programs to control and monitor processes.
MegaBasic programs may be developed off-line, using a standard text editor on a
personal computer, or on-line with a terminal attached to the PCM programming port.
A separate version of the MegaBasic interpreter also allows programs to be developed
off-line in the MS-DOS environment. The MS-DOS version, however, does not support
the PCM extensions to MegaBasic.
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A MegaBasic program must be loaded to PCM RAM prior to being run on the PCM. If
the program is saved to the PCM RAM Disk (RAM:), the PCM can be configured so that
the MegaBasic program is automatically copied into the MegaBasic program execution
RAM and executed by the MegaBasic interpreter upon power-up or reset.
RAM Disk
The RAM Disk is an area of RAM used to simulate a disk drive. It contains all memory
not used by MegaBasic. Like any other storage medium (hard disk or floppy disk), the
RAM Disk is used to store program and data files. RAM Disk files are preserved by a
battery when the PLC is powered off.
1-2 Series 90 Programmable Coprocessor Module and Support Software User’s Manual – November 1999 GFK-0255K