Mano base computer and the FGO flag
You may have a misunderstanding of OUTR. OUTR is not the R in the flowchart you posted. Here is what is exactly done in the Mano system:

OUTR is not flag! It's a register for sending AC's value to the output device.
FGO is a flag in system that shows whether the CPU is ready to send data to output device or not. So it is "1" by default. The CPU checks the flag:


If FGO="1" :  The device is ready to send output in an interrupt cycle! so R&lt;--1 and the interrupt process will start:  AC's content will be moved to OUTR in parallel and FGO="0" (means OUTR is full and you cannot send anything to output device!).
If FGO="0": means that the device is busy reading data from OUTR so no more data can be send out.


At the end of the I/O process the R&lt;--0 means get out of Interrupt cycle!