FUNCTION GENERATOR
Analogue shaping techniques are used in the AD639 to provide all normal trigonometric functions and their inverses. Selection requires only an input voltage representing an angle.
In this function-generator circuit, part of the 639's 12-page data sheet, frequency from 20Hz to 20kHz is voltage controlled and amplitude is within 0.1dB of 2V RMS. Amplitude modulation is possible using the U2 input.
Other applications in the Analog Devices data sheet are a four-quadrant sine/cosine multiplier and a sine/cosine oscillator. Connections for basic cosine, tangent and arctangent output are also given.
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DYNAMIC-RAM CONTROLLER
Two microprocessors can access the same bank of d-ram using the 74LS764 dual-ported controller.
Arbitration, signal timing, address multiplexing and refresh generation are performed by the 764 which, with nine address lines, can control up to 1M-byte of ram.
Note M86-1196/RST from Mullard details the device and shows three memory-sharing circuits, this one for two Z80 processors, one for a Z80 and 68000 and one for two 68000 devices.
Clock rates of up to 30MHz can be used; adjustable refresh timing is possible through use of a separate refresh clock section.
Provided that both c.p.u.’s operate from the same clock, the controller also allows priority to be given to a particular processor.
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(adapted from: Wireless World , Dec. 1986)