Scientific Calculator

The calculator of the present invention includes a clock mode in which the calculator accumulates and displays the time of day (real time) or, alternatively can be set to display the time events take place (stopwatch), the elapsed time between events or the elapsed time of several events beginning at the same time and ending at different times (splits). Operation of the clock mode is based on a substantially constant number of program instructions executed by the calculator every 100th of a second as controlled by a master oscillator.

FIG. 1 is a top view of a general purpose calculator having selective time-keeping and time data computing capabilities according to the preferred embodiment of the invention.

FIG. 2 is a block diagram of the calculator of FIG. 1.

FIG. 35 is a flow diagram showing the keys to be operated in performing functions when the calculator of FIGS. 1 and 2 is the clock mode.

FIG. 36 is a flow diagram of the program clock of the calculator of FIGS. 1 and 2 showing loops depicting hundredths of a second, seconds, minutes and hours.

FIGS. 3-34 and FIG. 37 may be found in the above incorporated U.S. Patent.

In the clock mode of the present invention, the calculator operates as a clock or a stopwatch which stores and displays split times. Referring to FIGS. 1, 2, 35 and 36, the clock mode operates as follows: a time of day is entered into the calculator display where the two digits to the left of the decimal point represent hours, the two digits immediately to the right of the decimal point represent minutes, the next two digits represent seconds, and the last two digits represent hundredths of a second. The clock mode is initiated by pressing Recall key (RCL) 118 followed by Enter key 116. Enter key 116 will always start the clock; Change Sign key (CHS) will toggle the clock and make it start or stop (whichever it is not doing when this key is pressed); Enter Exponent key (EEX) will blank or unblank the hundredths of a second portion of the display (whichever is not being done when this key is pressed), although the clock will continue running. The clear X key (CLX) clears the clock to zero, and the summation key (.SIGMA. +) always stops the clock.

Split times are stored by pressing a digit key while the clock is running, which stores the time at which the digit key is pressed in a storage register of the same number as the digit key pressed. If the clock is not running, pressing a digit key will recall the constant (e.g. previously stored split) in the register of the same number as the digit key pressed.

There are many applications for the clock mode of the present invention. For use as a stopwatch the clock is started when a race begins. When the first runner crosses the finish line, the "one" digit key is pressed and his time of arrival is stored in register one, without interrupting clock operation. When the second runner crosses the finish line, the "two" digit key is pressed and his time is stored in register two, and so forth up to 10 finishers. At the end of the race, pressing the summation key (.SIGMA.+) stops the clock. Pressing the digit keys corresponding to the respective arrivals then recalls the elapsed time for each runner during the race.

The clock mode is based on the characteristic that the same number of instructions are executed by the calculator every one-hundredth of a second as controlled by the 800 KHz oscillator 100. Referring to FIG. 36, loops 1, 2, 3, 4 and 5 each never contain more than 35 instructions which is equal to the time taken to increment the hundredths-of-a-second register. While 35 instructions are required to adhere to the clock standard, many fewer than 35 instructions are required to execute any loop of the program. Therefore, loop execution must include additional instructions equivalent to the difference between 35 instructions and the number of instructions required to execute the loop. However, the amount of delay, i.e. the number of no-op code or other instructions to be added that are unrelated to operation of the clock, is "loop-dependent", since the number of instructions required to execute each loop is different. For example, during execution of loop 1, which is executed when there is no carry in the hundredths-of-a-second register, the status of the keys associated with clock control on the keyboard is determined every one hundredth of a second until there is such a carry. During execution of loop 2, a few of the remainder of the 35 instructions available are used to zero the hundreds-of-a-second register and to add one to the seconds register. Every 59 seconds, a few more of the remainder of the 35 available instructions for execution of loop 3 are used to zero the seconds register and add one to the minutes register; every 59 minutes, some more of the remainder of the 35 available instructions for execution of loop 4 are used to zero the minutes register and increment the hours register; and finally every 12 hours a few more of the remainder of the 35 available instructions for execution of loop 5 are used to reset the hours register to one. Thus, every 12 hours the hundreds-of-a-second register is zeroed 360,000 times, the seconds register is zeroed 3,600 times and the minutes register is zeroed 60 times. Refer to U.S. Pat. No. 4,001,569.