2c1

4.5.4 Manual Control Interface (Left Side of Schematic Sheet 4):

The main component of the Manual Control Interface is multiplexer M8. This component acts as a two-pole four position switch, operated by address lines ADR6 and ADR7 from the microcomputer MPU. Table 4-1 lists the input/output relationship of multiplexer M8 with the given Address inputs. Multiplexer M8 interfaces the information derived from the game's various mechanically operated switches. These induce: two coin switches, two sets of four pushbuttons for controlling directions of arrow-movement, two START switches, the operator switches contained in miniature switch assembly SW1 (mounted in locations J8 and J9 on the PCB), and the Self Test Switch. All information is received by the microcomputer MPU when the MPU addresses the Address Decoderfor a low SWITCH Signal that enables tri-state device KS for a data output on the D6 and D7 data lines.

Coin information is a matter of storing in the microcomputer RAM the number of times a low logic level pulse appears on the data lines, when the appropriate address input of multiplexer M8 is being addressed. The microcomputer MPU only "looks" for coin pulses during the attract mode and the ready-to-play mode.

Arrow direction information is "looked" for by the microcomputer MPU during the play mode.

Switch information is received by multiplexer M8 at inputs ICO and 2CO. The microcomputer MPU addressed Decoders F9, H9, and J9 to determine if a switch is opened or closed. If closed, a low pulse will result for the given address as listed in Table 4-2.

5.55 Tone Generator (Top Right of Schematic Sheet 4):

The key to the Tone Generator is the operation of transistor Q1 in conjunction with timer D7,8. Timer D7,8 operates as an oscillator with output frequency dependent upon the resistive charge path of capacitor C22.

Varying the collector-to-emitter resistive value of transistor Q1 varies the combined resistive charge path of capacitor C22 through transistor Q1 and resistors R21 and R23 in parallel with resistor R22. As the combined resistive value decreases, the output frequency of the timer increases. Variable resistor R23 makes it possible for the operator to manually adjust the frequency for a desirable tone at the game site.

The conductance of transistor Q1 is varied by grounding any combination of voltage divider resistors R5, R6, R7, and R8. The combinations of these resistors are determined by data from the microcomputer RAM, applied to the input of Latch D4. Table 4-3 lists the approximate voltages at the base of transistor Q1 for the sixteen different address inputs. These addresses cause a latch condition of Latch 04 only if a low FREQ signal enables Latch D4.

Table 4-2

To derive a realistic tone, the output of Timer D7,8 is divided into separate frequencies by Divider

Addresses of Switch Positions for MPU Dala Line D6 D7 Input

Table 4-2

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