The divide-by-8 counter is triggered by the control flip-flop and clock, which then allows the data output register to begin storing the input data. Once all eight data bits are stored in the data output register, the data output register and the divide-by-8 counter trigger the one-shot. The one-shot then begins the process all over again.
It keeps track of the eight data bits, triggering the transfer of the data through the output register and the one-shot, which then resets the control flip-flop and divide-by-8 counter.
Once the data cycle is initiated by the Start bit, the one-shot produces an output pulse equal to the duration of the eight data bits. Once the eight data bits have been transferred to the data input register, the falling edge of the one-shot pulse resets the Control FF to start the sequence all over again.
After counting eight clock pulses equivalent to eight data periods, the terminal count of the divide-by-8 counter and the clock trigger the one-shot, which in turn resets the Control FF and divide-by-8 circuits to begin the sequence all over again. Simultaneously the data is transferred through the output register.
