GE PACSystems RXi User Manual page 55

Chapter 4. Configuration
Calculation of Memory Required for Managed Memory
The total number of bytes required for symbolic and I/O variables is calculated as follows:
Md = 3 or 4. The number of bits is multiplied by 3 to keep track of the force, transition, and
value of each bit. If point faults are enabled, the number of I/O discrete bits is multiplied by 4.
Mw = 2 or 3. There are two 8-bit bytes per 16-bit word. If point faults are enabled, the number
of bytes is multiplied by 3 because each I/O word requires an extra byte.
Calculation of Total User Memory Configured
The total amount of configurable user memory (in bytes) configured in the CPU is calculated
as follows:
Note:
42
[((number of symbolic discrete bits) × 3) / (8 bits/byte)]
+ [((number of I/O discrete bits) × Md) / (8 bits/byte)]
+ [(number of symbolic words × (2 bytes/word)]
+ [(number of I/O words) × (Mw bytes/word)]
Total managed memory (bytes)
+ Total reference words × (2 bytes/word)
+ [if Point Faults are enabled] (Total words of %AI memory + total words of %AQ
memory) × (1 byte / word)
+ [if Point Faults are enabled] (Total bits of %I memory + total bits of %Q memory) / 8
bits/byte)
The total number of reference points is considered system memory and is not
counted against user memory.
PACSystems* RXi Distributed IO Controller User Manual GFK-2816F