The First Figure is A Top Level Diagram showing the Serial Port and I/O Ports.
Fig.1 Top Level Diagram
This shows that the I/O port accepts input from the Control Module and the O-Bus, and communicates bi-directionally with the rest of the world. It also sends itís output to the B-Bus.
The serial port communicates bi-directionally with the outside world. The control module configures the internal timer which gives us a base Clock. The O-Bus sends data and the B-Bus is where data is put.
The O-Bus, B-Bus, and Control Module are all internal, predefined processor blocks.
Fig.2 Serial Port Block Diagram
As you can see from the above diagram the transmitter is much simpler than the receiver. The transmitter just clocks out whatever is put in the shift register. The receiver has a trigger that detects the beginning of a message, the Counter/Input Controller adjusts for the 16x overclocking. It is also double buffered to allow easy timing.
Fig.3 I/O Port Diagram
The Basic I/O Port Block Diagram is shown in figure 3. It simply puts out what is coming in on the O-BUS when enabled and clocks in the input when read.