Memory Volatility - GE 90-30 PLC Series Installation And Hardware Manual

5
Figure 5-3. CPU Serial Port Connector on Power Supply

Memory Volatility

The term volatility refers to the issue of whether or not a certain memory type retains or loses its
contents (data) when power is removed from it.
5-4 Series 90-30 PLC Installation and Hardware Manual – August 2002
This serial port is RS-485 compatible, and uses the GE SNP (Series Ninety Protocol)
protocol (slave only). Breakfree SNP became the default protocol on all serial ports on the
Series 90-30 CPUs, starting with firmware release 9.00 for CPUs 350–364, and firmware
release 8.20 for CPUs 311–341. For details, see page 5-13.
The serial port connector is only functional in a power supply that is installed in a baseplate
that also contains the CPU. It is not functional on a power supply that is installed in an
expansion or remote baseplate.
Any device connected to the serial port that uses +5 VDC power from the Series 90-30 power
supply must be included in the calculation for maximum power consumption (see the heading
"Power Supply Loading Calculations" in Chapter 12).
All Series 90-30 CPUs have this serial port arrangement. The 351, 352, and 363 CPUs have
additional serial ports, described in a later section of this chapter.
Care must be taken that common mode voltage specifications are met for
connections to this serial port. Common mode conditions that exceed those
specified will result in errors in transmission and/or damage to Series 90
PLC components. Common mode specifications are discussed in
Appendix A. When the common mode voltage specification is exceeded, a
port isolator such as the GE IC690ACC903 must be used. See
Appendix G for details on this port isolator.
Volatile memory - memory that loses its contents when power is removed. RAM memory is
inherently volatile. Therefore, when the PLC is turned off, a backup battery is necessary if
data loss in RAM memory is to be prevented.
Non-volatile memory - memory that retains its contents when power is removed. The various
types of PROM (Programmable Read-Only Memory) memory are non-volatile.
RS-485
COMPATIBLE
SERIAL PORT
Caution
GFK-0356Q