Casio AS-8A Calculator
The Casio AS-8A is a pretty early Vacuum- Fluorescent display calculator, introduced in September of 1971. This particular machine was manufactured in the late part of 1971, making it a rather early example of the machine. The AS-8A uses rather different 8-segment individual VF (Vacuum Fluorescent) display tubes. The display renders digits in conventional seven-segment form, with the exceptions being '4', which uses the eighth small segment to give the horizontal bar of the 4 an extra little tail to the right of the long vertical bar, and the other is the '0', which is shown in 'half-height' form. Aside from the somewhat unusual display elements, the Casio AS-8A is otherwise quite conventional for its time.
Profile view of Casio AS-8A with Cover
The AS-8A is a eight-digit, four function machine, with switch-selectable constant for multiplication and division. It can operate in floating decimal mode, or fixed decimal at 0, 2, or 4 digits behind the decimal point, as specified by a keyboard panel switch. The left-most digit in the display (there are nine display tubes) is used to indicate the error condition, and the sign of the number on the display. The keyboard uses magnet-activated reed switches, and connects to the main board via an edge-connector.
Casio AS-8A Internal View
The brains of the AS-8A are contained on a single circuit board mounted in the bottom half of the plastic case. The machine is based on a single-chip LSI IC, an HD3272, made by Hitachi. There are a couple of small-scale support IC's, along with some discrete component circuitry. The displays are driven by a Hitachi-made 'brick' that appears to be a hybrid device that apparently does the display encoding and driving. The logic is powered by a linear transistor-regulated power supply which is located across the back of the calculator, and connects to the main board via a small edge connector.
Closeup of Keyboard
The AS-8A performs the standard four functions. Addition and subtraction operate 'adding machine' style, with multiplication and division using the "=+" key to calculate the result, or the "=-" key to generate a negated result. The "AC" key clears everything, and the "C" key clears the display. The machine provides leading zero suppression, and does trailing zero suppression when in floating decimal mode.
The 8-segment VF Display of the Casio AS-8A
The AS-8A is not very fast, with the 'all nines divided by 1' benchmark taking about 1/4 second. Given that the clock frequency used to run the HD3272 calculator chip is only 30KHz, it's no surprise that it isn't a terribly fast machine. This is likely because of the early MOS technology used in the single-chip calculator implementation. Reduction of clocking speeds for early MOS Large-Scale Integration devices was quite common to improve the yields of these complex devices. During calculations, the displays are left active, with the left-most digit dimly lighting 'E' during the times the machine is busy. Division by zero causes and immediate error indication, signified by an "E" being displayed in the left-most display tube, the display being cleared to zero, and the keyboard locked out. The "AC" key must be pressed to clear error conditions. The machine has one fluke in its operation, in that numbers can only be entered with a maximum of seven digits behind the decimal point. For example, 0.1234567 is OK, but trying to enter 0.12345678 will result in an overflow (with E displayed and the keyboard locked). It appears that the leading zero before the decimal point is considered 'signficant' by the machine's logic.