Upgrading Clearfog Base to support CN9130 SOM
This guide is meant to explain how to upgrade the the ClearFog Base to support both CN9130 SOM and A388 SOM.
Removal of conflicting parts
Remove the components from table below:
# | RefDes | Qty | Action | Comments |
1 | R153 | 1 | Remove | RES 740ohm |
2 | U24 | 1 | Remove | 74LVC1G125GW |
3 | U26 | 1 | Remove | 74LVC1G125GW |
The components locations are marked green in the pictures below:
Components side
Print Side
Impact
The changes outlined partially impact functionality of the M.2 connector:
pin 6 (FULL_CARD_POWER_OFF#) is left floating
pin 67 (RESET#) is left floating
If an M.2 module is missing internal pull-ups, or has internal pull-down, it might permanently stay powered off or in reset.
As a workaround the IOs originally controlling the operational amplifiers U24 / U26 can be connected directly to M.2 connector using short wire, as shown below:
Workaround for floating M.2 control signals
FULL_CARD_POWER_OFF
Some LTE modules were found to have integrated pull-down for FULL_CARD_POWER_OFF, therefore the following workaround is recommended:
RESET
RESET is specified as a 1.8V signal for M.2, digital IO has 3.3V logic level.
Therefore no workaround is recommended.
If strictly required, operation may be safe in open-drain configuration as long as software behaviour is validated first.
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