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Serial Communications
Options and Non-volatile Memory
There are many different types of memory used in computer driven devices. The terms RAM (random
access memory) and ROM (read only memory) are a couple with which you may be familiar.
RAM is used in computers to run programs and hold data for a short period of time. This is the mem-
ory that is used primarily in PCs. RAM is very fast and can be read and written to over and over again.
ROM is used in computers to hold the ‘permanent’ programming that allows a PC to start. This mem-
ory is ‘burned in’ to the chip itself and can not be changed. Unlike RAM, however, this memory is per-
manent. While it can not be changed, it can not lose its programming when power is turned off.
There is a third type of memory that is now currently used to combine the characteristics of both RAM
and ROM. This is known as EEPROM (electrically erasable programmable read only memory). While
the name may be long and somewhat cryptic, the EEPROM can be erased and re-written many times,
and yet hold the programmed data even over long periods of time when the power is off. This is the
type of memory that all Love Controls uses to save the settings your program in your control. The reli-
ability and longevity of the data retention is what allows us to guarantee a 10 year data retention with-
out power.
In normal operation, the control uses RAM, just as any other computerized device. Whenever you
make a change to one of the parameters in the control, the set point for example, the new value is writ-
ten into the EEPROM. This way, if power goes off for whatever reason, when power resumes, the lat-
est settings are preserved. When power is turned on, the data is copied from the EEPROM to the RAM
to begin operation.
If EEPROM is such a wonderful thing, you might ask, why bother with RAM? One reason is that RAM
is much faster than EEPROM. Faster speed gives you better performance in critical control functions.
Perhaps the most important reason is that EEPROM has a limit to the number of times it can be erased
and re-written. Current technology now sets that limit at about one million erase/write cycles. In a
dynamic control situation, it may be necessary to update RAM every few milliseconds. EEPROM can
not keep up to that pace, and, even if it could, it would be ‘used up’ in a matter of days.
If you think about how long it would take a million changes to the control programming through the front
key pad, you will see that it would take a very long time to get to use up the life of the EEPROM.
Adding one of the computer communications options (e.g. 992) changes the picture. The speed of
computer communications is such that hundreds of instructions can be made in less than a minute. In
such a situation, the million erase/write cycles could be used up in a couple of months causing the con-
trol to fail.
Usually in such a situation, the control is under close observation by the host computer. It may not be
necessary, then for the data to be written to the EEPROM, as it is ‘transitory’ in nature (changing set
points for a ramp/soak sequence for example).
All 32A Series controls with communications options made before April 2001 are only able to write to
the EEPROM. Controls manufactured after this date have a menu item in the Secure menu (
Stor
) that
allows the serial communications to write to RAM (
Stor = no
) with a special write command that allows
the EEPROM to be updated or written directly to EEPROM (protocol command 0442). The anti-reset
windup (ArUP) must be on to insure no memory is stored.
The factory default is ‘write to EEPROM’ (
Stor = YES
).
Содержание LOVE CONTROLS 32A Series
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