Ram Memory; Ram Memory Backup/Backup Battery Information; Programmable Read-Only Memory (Prom) Types; Uses Of Prom Devices In The 90-30 Cpus - GE 90-30 PLC Series Installation And Hardware Manual

RAM Memory

Every Series 90-30 CPU uses RAM memory for its "working memory." The RAM chips used are
of the CMOS type. CMOS RAM is an acronym for Complimentary Metal-Oxide Semiconductor,
Random Access Memory. CMOS RAM is a relatively fast, low power memory that can be easily
examined (read) and changed (written to).
In the embedded CPU models, RAM memory is mounted on the backplane board. In the modular
CPU models, RAM memory is mounted inside the CPU module. A backup battery is usually used
to preserve the contents of RAM memory when power is off.

RAM Memory Backup/Backup Battery Information

Please see Chapter 6 for the following information:

Programmable Read-Only Memory (PROM) Types

There are three types of PROM devices used in Series 90-30 CPUs:
EPROM: Erasable Programmable Read-Only Memory. It is a plug-in integrated circuit memory
device that can be erased with an ultraviolet light. EPROMs can be read when installed in the PLC,
however in order to write new data to them, they must be removed from the PLC and written to
using an external PROM burning device.
EEPROM: Electrically Erasable Programmable Read-Only Memory. It is a plug-in integrated
circuit memory device that can be erased and written to while installed in the PLC.
Flash Memory: A variation of the EEPROM type memory. It also is an integrated circuit device
that can be erased and written to while installed in the PLC. One advantage of CPUs having flash
memory storage of firmware, is that firmware can be updated by writing from a Personal Computer
through a PLC serial port to flash memory. No modules have to be removed for flash firmware
upgrade.

Uses of PROM devices in the 90-30 CPUs

PROM-type devices are used in two ways in the 90-30 CPUs:
The following table shows the types of PROM devices each CPU uses.
GFK-0356Q Chapter 5 CPUs
RAM memory backup recommendations.
Backup battery information such as estimated life, replacing, determining battery age using
date codes, etc.
Running without a backup battery.
Low battery warning methods.
To store CPU firmware
To store user data, which consists of program, configuration, and register data.
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