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244 Part 3 The instruction-set processor level: variations in the processor

Section 4 Desk calculator computers: keyboard processors with small memories

Fig. 2. Display in fixed point with the decimal wheel set at 5. The Y register has reverted to floating point because the number is too large to be properly displayed unless the digits called for by the DECIMAL- DIGITS setting are reduced.

4.398 364 291 x 10-3 = .004 398 364 291

The operator may choose to display numbers in FLOATING POINT or in FIXED POINT. The FLOATING POINT mode allows numbers, either positive or negative, from 1 x 10-99 to 9.999 999 999 X 1099 to be displayed just as they are stored in the machine.

The FIXED POINT mode displays numbers in the way they are most commonly written. The DECIMAL DIGITS wheel allows setting the number of digits displayed to the right of the decimal point anywhere from 0 to 9. Figure 2 shows a display of three numbers with the DECIMAL DIGITS wheel set at 5. The number in the Y register, 5.336 845 815 x 105 = 533 684.5815, is too big to be displayed in FIXED POINT without reducing the DECIMAL DIGITS setting to 4 or less. If the number is too big for the DECIMAL DIGITS setting, the register involved reverts automatically to floating point to avoid an apparent overflow. In FIXED POINT display, the number displayed is rounded, but full significance is retained in storage for calculations.

To improve readability, 0's before the displayed number and un-entered 0's following the number are blanked. In FLOATING POINT, digits to the right of the decimal are grouped in threes.

Pull-out instruction card

A pull-out instruction card, Fig. 3, is located at the front of the calculator under the keyboard. The operation of each key is briefly explained and key codes are listed. Some simple examples are provided to assist those using the machine for the first time or to refresh the memory of an infrequent user. Most questions regarding the operation of the Model 9100A are answered on the card.

Data entry

The calculator keyboard is shown in Fig. 4. Numbers can be entered into the X register using the digit keys, the p key or the ENTER EXP key. The ENTER EXP key allows powers of 10 to be entered directly which is useful for very large or very small

Fig. 3. Pull-out instruction card is permanently attached to the calculator and contains key codes and operating instructions.

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