Early Electronic Calculator Casio AL-1000 Calculator Technical Description: The T State Machine

	Figure 1: T State Machine Graph

The T state machine is a small 4-state machine. The states are:

• TSDISP: The calculator is simply in the multiplexing display loop. This is the idle state of the machine.
• TSFETCH: Fetch a program instruction and load it into the U latch for execution.
• TSFCT: Function Execution. Entered to execute a function whose code has been loaded into the U latch, by either the pressing of a function key or during program execution.
• TSNML: Numeral Entry. Entered when a numeral key (0-9) is pressed.

Figure 1 presents the state graph for the T machine. Note TSFCT can be entered either by a keypress or for program instruction execution. During TSFCT, the function execution state machine is enabled to perform the appropriate procedure. At the end of the procedure, some set of procedure-dependant conditions produces the STEND (STate END) condition, which results in the TSFCT state being exited.

Program execution is initiated by pressing the ADD key with the program switch in RUN mode. The TSFETCH state is entered for one number cycle. At the beginning of the cycle the DP counter is loaded with the decimal point digit of the program storage register, and the decimal point digit is incremented on it's way through the arithmetic unit to be written back to core, so accomplishing the program counter increment. During the fetch number cycle the DP counter is cycled, when it hits zero the current digit data (instruction function code) from the program storage register is loaded into the U latch. The U latch now being non-zero, the T state machine switches to TSFCT at the end of the fetch number cycle, to execute the function. The completion of the function (STEND again) results in TAB being loaded with the TSFETCH state code.