Early Electronic Calculator Casio AL-1000 Calculator Technical Description: Numeral Entry

The procedure for numeral entry is very similar to that of function execution. KNP (rather than KFP) triggers the start of a single shift-left state cycle. The T state goes to TSNML rather than TSFCT. The presence of KNP is used to force the T state back to TSDISP (display) after one state cycle. The function execution state machine remains in state 0 (idle) during this cycle. Figure 1 shows the complete timing of a numeral entry.

The state cycle is a standard shift left cycle, but with some additional actions. During DGT2 time, the A latch is loaded with the new numeral from the keyboard, and is so entered as the LSD of the number in the display. The decimal point position may or may not be incremented (via carry injection during DGT1), depending upon the state of the FDP flag which indicates whether the decimal point key has been pressed.

The FN flag is used to clear the display at the beginning of entry of a new number. The FN flag is set to 1 when an operation is performed and set to 0 by the press of a numeral key. With FN 1 the loading of digit data from core into A is suppressed during TSNML, so the first press of a numeral key after an operation results in the displayed number being cleared from the X register.

Figure 1: Numeral Entry State Cycle