Operations Manual

OPERATIONS 4-4
O&M of the MCC-545B PACKET DATA RADIO
12/2000
factory when the unit is first manufactured. The ROM can only be changed by replacing the chip
with one programmed with the new data.
Second, the RAM contains all dynamic data for the 545B. Any data logger data, positional data,
messages, etc. entered into the 545B are stored in RAM. Also, any command parameters - such
as configuration changes are stored in RAM. But RAM is volatile. It can only retain information
while power is applied. Normally turning off or disconnecting power would cause all RAM
information to be lost. In order to prevent this, a small internal NiCad battery is used to maintain
power to the RAM when external power is off.
So for normal operation of the 545B, the software operates from the data and parameters in the
RAM - even when power has been turned off for several days, then back on. Unfortunately, there
are always situations where the RAM data is lost or corrupted. For instance, it the 545B is being
stored, the jumper for the NiCad battery should be removed to prevent total discharge of the
battery over time. Or the software may fail (crash) and invalidate the RAM data. Or the user may
want to clear everything out and start over. Since we do not want these cases to lose our
configuration data, we have a third type of memory.
The third type of memory is EEPROM. It is nonvolatile (retains data even when power is
removed) and needs special access to program – thus it is not easily corrupted. The 545B can
retain a copy of all configuration parameters in EEPROM. But EEPROM is limited to 10,000
write cycles per memory location so the 545B only writes to EEPROM on special commands -
"ID" and "SAVE". And then only values that have changed are written. A validation checksum is
saved in the 545B to verify its data is correct.
When the 545B ships from the factory it is in a default configuration. The Operator Port (port 0)
is set for 9600 baud, 8 data bits, 1 stop bit, no parity, ASCII protocol, no flow control. This
provides a known starting point for communicating with the unit with a terminal or computer.
From this point, the user can enter the unit ID and other operational parameters and then enter
the "Save" command to write them to EEPROM. Note that as soon as parameters are entered
they take effect, BUT once the software is rebooted or restart due to a crash or failure of the
battery backup RAM, all changes will be lost unless they are saved in EEPROM.
Saving and Restoring Configuration - The Operation
Thus, the sequence is as follows -
1. The software normally executes using data and parameters from RAM. When the unit is
turned off or power is disconnected, the RAM information is maintained by battery
backup. When main power is restored, the unit continues operation from RAM.
2. If the Reboot command is issued, the white Reset button (S1) is pressed, the internal
battery backup is disconnected (by removing jumper JP1 while external power is off), the
NiCad battery fails or the software crashes and restarts, the RAM contents is lost. The
software detects this and copies the values in EEPROM into RAM when it continues
operation.