GE 90-30 PLC Series Installation And Hardware Manual page 126

Additional Serial Ports (CPU351, CPU352, CPU363)
Although all Series 90-30 CPUs have a serial port that is accessed through the connector on the
power supply, the CPU351, CPU352, and CPU363 each have two additional serial ports. The
connectors for these additional serial ports are mounted on the front of each CPU. These two built-
in serial ports eliminate the need for the CPU to access serial ports across the PLC backplane,
resulting in better system performance. These two ports support the SNP/SNP-X master and slave
protocols (see "Breakfree SNP Protocol" on page 5-13.), RTU slave protocol (in Firmware Version
8.0 and later), and the Serial I/O feature (in Firmware Version 8.0 and later) that lets you create a
custom serial output. Instructions on how to use these ports can be found in the Series 90 PLC
Serial Communications User's Manual, GFK-0582C or later.
Floating-Point Math
All Series 90-30 CPUs can work with integer numbers. (The set of integer numbers consists of all
positive and negative whole numbers, including zero.) The floating-point math feature enables a
CPU to work with decimal numbers in addition to integer numbers. It also provides trigonometric,
logarithmic, exponential, and radian conversion functions. Floating-point math is also referred to as
"real number" math. The CPU352 and CPU374 have always had hardware-based floating-point
math capabilities due to the built-in math co-processor chip. Starting with CPU firmware release
9.0, all of the other CPUs in the 350–364 CPU group were provided with firmware-based floating-
point math capability. Although there is a speed difference between the hardware-based floating-
point math of the CPU352 and CPU374 and the firmware-based type, this will not be significant to
many users. For applications where faster performance is important, the CPU352 and CPU374 are
the best choice. The floating-point math instructions are explained in the Series 90-30 PLC CPU
Instruction Set Reference Manual, GFK-0467K or later.
Flash Memory
All of the 350–374 CPUs have built-in Flash memory, which serves two purposes:
Keyswitch
All 350 – 374 CPUs have a keyswitch; however, some versions of the CPU firmware do not
support all of the keyswitch features (see the section "Determining CPU Revision Levels" earlier in
this chapter). These differences are described in this section. Note that the keyswitches on some of
these CPUs are labeled ON/RUN and OFF/STOP and on others are just labeled ON and OFF.
Regardless of the labeling, all of these keyswitches work as described below:
GFK-0356Q Chapter 5 CPUs
It provides non-volatile storage of the CPU firmware.
It gives you the option of storing program, configuration, and register data in non-volatile
Flash memory. Two ways of using this memory are: (1) to store an on-board backup copy of
user memory (although we still recommend that you keep a separate backup copy of your
complete program folder), and (2) for running in a battery-less scheme. For details, please see
Chapter 6.
Flash Memory Protection: This standard, hard-wired feature can be used to prevent Flash
memory from being changed by unauthorized people (people without a key). When the key
switch is in the ON position, Flash memory cannot be changed (written to). This keyswitch
feature will always be in effect, regardless of how the next two configurable features are set.
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