Mamiya 645 AFD - Manual (Page 5)

Condition #6
When the digital back or host computer is busy, this indicator will be
displayed. If the shutter release is pressed the -no- db indication (see
condition 7) will be displayed and blink for 3 seconds.
Condition #7
If the digital back is connected to the Mamiya 645AFD and the connec-
tion to the host computer is not installed, this will be displayed when
the shutter release is pressed. This will also appear under the previous
three conditions when the shutter release is pressed.
Internal LCD External LCD