Firmware names:

The firmware files have the following naming structure:
  Protocol - ModelName - ModelNumber - Feature . hex
for example:
  SQM-LE-4-3-19.hex

ModelName:
 SQMLE: firmware for Ethernet model (SQM-LE) and USB model SQM-LU
 SQM-LU-DL: firmware for datalogging unit (SQM-LU-DL)

Protocol:
  4=is the most recent

ModelNumber:
  3=SQM-LE/U
  4=SQM-C
  5=SQM-LR
  6=SQM-LU-DL
  7=SQM-GPS (reserved for GPS model)
  9=SQM-B (reserved for Bluetooth model)
 11=SQM-LU-DL-V
 12=SQM-HDR (reserved for High Dynamic Range)
 13=SQM-LU-DLS (snow LED firmware)

Feature:
80 (20220915)
  DL: add new DS1390U RTC type.
79 (20210428)
  LR: add accessories handlers
78 (20200525)
  Debug: DL,0123456789x log value of 32 bit input.
77 (20200309)
  DLS: rFx now shows raw uncompensated full frequency with period mode results converted to frequency also in one value.
76 (20200307)
  DLS: remove temperature compensation from raw frequency ouput used by rFx request.
75 (20200305)
  DLS: inline raw frequency rFx request added.
74 (20191230)
  V: power down accelerometer when sleeping.
73 (20190930)
  DL: bugfix to solve irregular trigger problem when supercap is drained and alarm values get cleared out.
72 (20190911)
  DLS: Clear out four empty std freq, snow rdg, snow freq registers at byte 16,20,24 in DL record in case snow readings are not enabled.
71 (20190910)
  DLS: Clear out four empty registers at byte 28-31 in DL record.
  DLS: Large Std,Snow frequencies reported as unsigned instead of cropped signed.
70 (20190731)
  DL: bugfix, do not sleep for log on x seconds. This stopped working sometime after version 56.
69 (20190723)
  DL: set subsequent flag while logging and powered by PC.
68 (20190705)
  DL: allow logging while connected to USB data cable
67 (20190627)
  DL/DLS: DL model firmware ver 66 was actually DLS model for a while. This removes the confusion.
66 (20190609)
  DL: Snow logging done in one larger 32 byte record. Requires latest UDM (after 20190609) to read.
65 (20190501)
  DL: Logging threshold is respected again after being ignored in version 61-64.
64 (20190318)
  DL: Allow Log one snow reading from non-ideal-crossover firmware.
  DL: Linear frequency output report limited to 25kHz (value still scaled up by multiplier of 45000)
63 (20190317)
   DL: Internal DL change: Only save 8 bit battery voltage since it is only 8 bits anyway.
   DL: Snow logging combined into one free byte of DL record.
   New command: rfx reports light flux (a value equivalent the frequency of the light sensor). The dark frequency has been compensated for.
62 (20190112)
   Feature: Added Snow LED logging and control (A5ex).
61 (20190106)
   Feature: Added Snow LED status A5x.
60 (20181122)
   Feature: HDR I2C interface added.
59 (20180905)
   Feature: color model, option to cycle colors after each reading.
58 (20180721) 
   Feature: Add r1x which reports both averaged and unaveraged values as well as fresh/stale state.
57 (20180207) 
   Bugfix: DL: subsequent readings were ~0.66 brighter
56 (20171019)
   Vmodel fix: log record report containd extra comma before Acc readings.
   LE relay output fix: anything but manual caused extra reading reports.
55 (20171008)
   Test: added bank setting in command response area, no functional update.
54 (20170927)
    All-bugfix: Reporting compressed fixed to only report "compressed" reading.
53 (20170916)
    All-bugfix: Prevent psuedo-lockup when DisplayEnabled and ReportingEnabled and ReportingCompressed.
52 (20170815)
    color model, fix hang when too bright.
 51 (20170713)
    LED accessory apostrophe lights up when relay accessory is on. And prevent extra rx result when only display needs updating.
 50 (20170420)
    DL command LIx now returns m suffix for logging minutes.
 49 (20170420)
    DL bugfixes:
      - connection at :50-:57 seconds stalled for new RTC.
      - bugfix Initial false recording on USB connection not made anymore.
    DL features:
      - LED fading (~1 sec duration) to indicate wake from sleep every minute.
      - Initial and subsequent records marked separately.
 48 (20170406) DL bugfix - "Every x minutes" mode made records while connected to PC, fixed.
 48 (20170316) Addition of snow detection LED control to LE model.
 47 (20170203) DL retrieve all packets use pre-request flow control now to fix retrieve loss on slow computers.
 46 (20161216) LE Lock switch options added allows fine grain security control.
 45 (20161207) reply blocks sent in short loop to reduce retrieve-all time.
    - Fix LED accessory options always blinked when reading was requested.
 44 Added display accessory mode to update only at reading request. Reduce display accessory models from 0-7 to 0-3 to allows mode bit.
 43 Added code for solid state relay accessory control.
 42 Lock recognized for Report Interval settings to prevent undesired setting.
 41 Accessories added to LE/LU/LR models. Humidity/temperature, display, LED.
 40 (201607__)
    - Continuous reporting feature added, with optional LED blinking to indicate reading taken.
 39 (20160603)
    - V model - read accelerometer magnetometer values contiguously to reduce spurious values.
 38 (20160225)
    - Bug fix from ver37 that prevented old DL RTC from working. Loading of variable RTCCTL registers was mixed up.
    - Put the 4uS RTC delay into all CE on/off settings instead pof just the off settings and some on settings.
    - remove unneeded RTC delays from between address and data writing.
    - RTC version reported in command Lvx
 37 (20160204)
    - initial test for DL optional added DS3234SN# RTC
 36 (20151211)
    - Bugfix: DL "Retrieve All" had spurious values. 
 35 - All: Add stored model information parameters for Lensholder, Lens, Filter.
 34 - DL: fix low-memory EEPROM to identify that >32768 records can be made
        which worked fine in ver25, only an issue if updating firmware on
        a unit with stored records .
    - DL: Add diagnostic L7x to report bytes per FLASH, bytes per record.
 33 - Clear OERR in receive routine because continuous streaming of commands
        can lock up unit during Vector monitoring (calibration mode).
 32 - Vector: flash LED after logging a reading
    - Vector: bugfix; logging of Mz corrected
 31 - Bugfix: Vector; block simultaneous command and interrupt SPI usage.
 30 - Bugfix: DL max record size calculations modularized for various models
        and memory chips
    - Bugfix: DL mode xSec,xMin produced unnecessary CRLF. Removing this
        allows DLRetrieve and these modes to operate at the same time.
 29 - DL power save logging fixed (i.e. 5 minute on battery),
      unreliable FLASH release-power-down fixed.
    - Period mode to freq mode at 10Hz fixed negative sign detection
    - DL updated for Vector records of 32bytes
 28 - Vector model wiring change to accommodate future GPS
 27 - DL EEPROM erase blocking removed, use command L6x to see status now
    - Added FLASH power-down
 26 - Allow more than 64char commands (up from 32)
 25 - DL fix Retrieve log report data corruption
 24 - DL added code to pause RTC
 23 - DL fix of dark recordings on battery power
 22 - buffered cells reported "UX"
 21 - Enable filtered period to remove jitter
 20 - DL (data logging) synchronized to RTC
 19 - simulate calculations added
 18 - filtered period to remove jitter

