Memory Protection - S-COM 6K Owner's Manual

frequency in the range of 100 Hz to 3000 Hz, with an accuracy of a few Hertz. CW amplitude and
paging amplitude are separately adjustable with pots.
DTMF characters are generated via the encoder portion of the MT8880 DTMF Transceiver IC.
DTMF paging amplitude is pot-adjustable. DTMF dialing amplitude is not adjustable, and is fixed at
the level set by FCC Part 68 regulations.
9.

MEMORY PROTECTION

The controller contains circuitry to protect the data stored in RAM and maintain the data during
power outages. A DS1210 IC monitors the 5 V logic supply; when it detects an out-of-tolerance
condition, the IC disables the RAM's chip-enable input. It switches the RAM's Vcc input from the
logic supply to the lithium battery when the logic supply falls too low to maintain data integrity. The
lithium battery has a lifetime of over 5 years (10 years if kept at room temperature), since the
amount of current drawn by the RAM is very low under backup conditions (a few microamperes).
10. VOLTAGE MONITOR AND WATCHDOG TIMER
The controller contains circuitry to properly start the microprocessor when power is applied, to stop
the microprocessor when power fails, and to restart the microprocessor if it gets into a runaway
condition from a spike or transient.
A DS1232 IC monitors the 5 V logic supply and asserts the microprocessor's reset input when the
supply is out of tolerance. This method is superior to simple RC reset circuits, which may not
properly reset the CPU after voltage sags (brown-outs). The reset signal that is generated by the
DS1232 drives not only the microprocessor but also other ICs to ensure that the controlled loads
will be turned off, and that a graceful power-down sequence will be observed.
The DS1232 also monitors a software-generated "watchdog" signal. This signal is created at
intervals by the execution of the microprocessor's software program. If the CPU fails to execute the
program correctly, the watchdog signal will not be generated. The DS1232 will time out in less than
one second if it does not receive the watchdog signal, and it will force the microprocessor to restart
the program.
6K V1.02 03-16-91
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