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Technical Description
Program Memory (Internal Program Memory, Memory Submodule)
The control program is stored in the memory submodule or in the internal program memory
(RAM). The CPU 943 and CPU 944 can hold the entire program in internal RAM.
To safeguard against losing the program, dump it in an external EPROM or EEPROM memory sub-
module. In contrast to these memory submodules, the internal RAM or a RAM memory submo-
dule has the following characteristics:
•
The memory contents can be changed quickly.
•
User data can be stored and changed.
•
When the power fails and there is no battery, the memory contents are lost.
Process Images (PII, PIQ)
Signal states of input and output modules are stored in the CPU in "process images". Process
images are reserved areas in CPU RAM.
Input and output modules have separate images as follows:
•
Process input image (PII)
and
•
Process output image (PIQ)
Serial Interface
You can connect programmer, operator panels and monitors at the serial interface. You can also
connect the SINEC L1 local area network at the serial interface on all CPUs. You can order CPU 943
and CPU 944 with a second serial interface. The following additional functions are possible at this
interface:
•
Point-to-point connection to other programmable controllers
•
ASCII driver for connecting printer, keyboard, etc.
•
Integral real-time clock (see Chapter 13);
CPU 944 only:
•
Communications link (3964/3964R line procedure; see Chapter 12)
Timers, Counters and Flags
Each CPU provides the control program with internal timers, counters and flags. Flags are memory
locations for storing signal states. Timers, counters and flags can each be set as "retentive" (by
area), i.e. their contents are not lost at POWER OFF. Memory areas whose contents are reset at
POWER OFF are "non-retentive".
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S5-115U Manual
EWA 4NEB 811 6130-02b
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