Micromod MOD: 1800P - MOD 30ML Identity Module (Version 2) System, I/O and Communications Functions - Manual (Page 23)

Logic Functions - Book 1
DATABASE DESCRIPTION
2-11
2.4.4 LEDs
The LEDs on the main board are handled as follows:
both off =No power.
green off, red on =Initial Power-up condition, or Watchdog (not talking to I/O, default
state, etc.).
green on, red off =Normal; Running main database and talking to I/O.
green on, red on =Any instrument state other than RUN (eg. HOLD, UPLOAD, etc.). If
red LED stays on after power-up, fallback occurred and I/O
goes into failsafe.
green on, red flashing =Upload failure; Indicates failed attempt to upload main database to
instrument using switch on memory module.
2.4.5 Control contention
Control contention applies to write messages. Control is only given when a TAKE CONTROL
or OVERRIDE CONTROL message is issued. Control is then held by that source until: 1
minute expires since last write, or a RELEASE CONTROL message is received, or an
OVERRIDE CONTROL message is received.
2.5 SECURITY AND INTEGRITY FEATURES
2.5.1 End of configuration Checks
A downloaded database is checked and verified by the configurator. End of configuration
(EOC) checks on the instrument are therefore limited to checking the hardware I/O
configuration against what is specified in the database.
If it is determined at end of configuration time that the I/O configuration does not match what is
specified in the database, a diagnostic event is generated, and the instrument comes up in a
non-run state.
2.5.2 Checksumming
In an attempt to maintain integrity of both the main database memory and the portable backup
memory, checksums are generated for both memories. The main and backup memories are
divided into segments and a checksum value is maintained for each segment when the
database is created. The checksum value is the exclusive ’or’ (XOR) of all of the four-byte
words in the segment. The end of the segment is called the checksum boundary.
Checksums are stored in a table containing one entry per checksum boundary. When new
values are written to a database segment, the old values are XOR’ed out of the checksum
table entry for that segment, and the new values are XOR’ed in. The main memory checksum
table is used for this operation; the result is then copied to the backup memory checksum
table.
Checksum values are verified by checking one segment every 250 ms. First the main
memory segments are checked, then the portable ram segments are checked. If a checksum