The GX5055 board has three basic operational states; Halt, Pause and Run. The figure below is a block diagram showing the relationship of these operational states.
The GX5055 board goes into a Halt state after a Reset signal and following the Halt command. All external event inputs as well as external control inputs are ignored following a Halt command. Following Reset, all I/O pin (channels) are in the receiving mode of operation. The program counter is zero, the frequency is set to an internal 5MHz, and the strobe timing is set to 5ns.
The board enters a Pause state from a Halt state with an ARM command sent by the PC bus, or from the Run state following the Pause command.
In the Run state, data is being outputted and input data is being latched. The program counter holds the address of the current output and the address of the command to be decoded and executed by the sequencer. While executing the command, output pins send the data from the output memory located at the program counter address in the control memory and the input pins receive the data. The sequencer executing the command usually increments the programs counter by one unless the command changed the value of the program counter (for example, the Jump command) or the state of the machine was changed (for example, the Pause command). After changing the program counter value, the input data is stored in the input memory at the new program counter address.