Step 4: Selecting A Cpu - GE 90-30 PLC Series Installation And Hardware Manual

12

Step 4: Selecting a CPU

Once you have determined how many and what type of I/O and Option modules you require, you
can select a CPU. Many of the factors that apply to selecting Option modules, such as
performance, cost, standardization, etc. also apply to selecting a CPU. Details on CPU capabilities
are found in the "CPUs" chapter.
12-4 Series 90-30 PLC Installation and Hardware Manual – August 2002
Number of modules required by the system - Embedded CPUs come in 5-slot or 10-slot
sizes and they do not support Extension or Remote baseplates. Therefore, if a system requires
only a few modules, these may be an option. If more than 10 modules are required, you must
select a Modular CPU. The CPU331-341 CPUs support up to 5 total baseplates, and the
CPU350-364 CPUs support up to 8 total baseplates. If you need more than 49 total Option and
I/O modules, you will need to use one of the CPU350-364 group of CPUs.
Modules with Quantity Restrictions- Many modules are restricted as to how many may be
used in one system. This number also varies by CPU. For example, in the case of an
8-channel Analog Output module, the maximum number per system is:
4 if using a 311, 313, or 323 CPU
8 if using a 331, 340,or 341 CPU
79 if using a 360-364 CPU
Please see the section "Maximum Number of Modules Per System" for data.
Types of Option Modules - The PCM, ADC, CMM, and SLP modules can only work in a
Modular CPU baseplate. Use of these modules therefore rules out the use of Embedded CPUs
(311, 313, 323). See the section "Location of Modules in the PLC Racks" for more
information.
Performance - as shown in the "CPUs" chapter, the CPU350 - 364 CPUs use a more powerful
microprocessor than the lower numbered CPUs. For applications where higher performance is
required, one of these would be a good choice. For math-intensive applications, the CPU352,
with its built-in math coprocessor, would give the best performance. For Ethernet applications,
the CPU364 with its built-in Ethernet interface, provides faster performance than separate CPU
and Ethernet modules. This is because the separate modules have to communicate over the
PLC backplane, which is slower than the CPU364's internal path. For a similar reason, when
using serial communications, the CPUs 351, 352, and 363 (using Ports 1 and 2) perform faster
than a separate serial communications module (IC693CMM311) and CPU combination.
Extended features - The IC693CPU364 has a built-in Ethernet interface which would
eliminate the need for a separate Ethernet module. This would save a PLC slot. The CPU351,
CPU352, and CPU353 each have two additional built-in serial ports which eliminate the need
for a separate serial communications Option module. The CPUs 350-364 have extra features
and capabilities that the other CPUs do not have such as, Floating Point Math, Sequential
Event Recorder, and Memory Protect Key Switch. Also, CPUs 351-364 have larger total
memory size, as well as configurable analog and register memory.
Memory requirements - The CPU351-364 CPUs have configurable analog and register
memory. This makes them more capable of meeting the needs of Option modules that require
this type of memory and user programs that require larger amounts of register or analog
memory. The CPU360 does not have configurable memory and has a lower base memory size
than the CPU351–364 CPUs. The CPU360–364 CPUs have standard Flash PROM for user
GFK-0356Q