Handbook of air conditioning and refrigeration / Shan K

attery backup. However, EEPROM cannot be used for as many writing, erasing, and rewriting
cycles as RAM.
● Flash erasable programmable read-only memory (flash EPROM), which is a kind of new memory
technology and allows the stored control software to remain untouchable indefinitely without
power.
System controllers often use a 16-bit microprocessor. A typical system controller has the following
memories:
RAM: 256 Kbytes
ROM: 128 Kbytes EEPROM
512 Kbytes flash EPROM
ENERGY MANAGEMENT AND CONTROL SYSTEMS 5.25
FIGURE 5.14 A typical unit controller. (Source: Honeywell Inc. Reprinted by
permission.)
Input/Output (I/O). There are four kinds of I/O: analog input (AI); digital or binary input (BI);
analog output (AO); and pulsed or binary output (BO). Conventionally, a sensor input, a controller
output, or a control value, is referred to as a point or object. Current system controllers allow their