If the folder queried is empty without any files, the module will report an error and the data 7E FF 06 40 00 00 06 FE B5 EF will be
returned.
4.6.4 Query total folder numbers in current storage device
Query total folder numbers in current storage device 7E FF 06 4 F 00 00 00 FE AC EF
Users can query the total folder numbers of the current storage device through sending the command above. This just supports to
query the folder numbers under the root directory of the device. Not possible to query the sub-folder numbers (Please do not build
any sub-folders under a folder).
4.7. About Delay of Serial Programming
1) After the module is powered on, it needs about 500ms to 1500ms (depending on the track quantities in the
storage device) to initialize. After that, some data related to initialization returns to MCU. Users can choose to
ignore these data.
2) After specifying playback of a device (SD card or USB flash), it needs 200ms delay before s ending the
command to execute the relative operation.
3) The module processes a serial data per 10ms, so when MCU continuously sends commands one by one,
20ms delay must be added before sending next command, otherwise the command MCU sends out will not
be executed.
4) If specifying playback of a track in a folder, the delay must be longer than 40ms, as it needs time to target a
track in a folder. And even so song as sending the commands related to query a track or a folder, 40ms delay
is required.
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