Microprocessor having a dynamic memory refresh circuit

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365222, 36424691, G06F 100

Patent

active

049243810

ABSTRACT:
A microprocessor includes an execution unit executing a program according to an instruction, an instruction prefetch circuit storing a plurality of instructions to be executed by the execution unit, a refresh control circuit controlling a refresh operation of a dynamic memory coupled to an external bus and a control unit. The control unit receives bus access request signals from the execution unit and from the instruction prefetch circuit, respectively, and a refresh request signal from the refresh control circuit and sends a refresh grant signal to the refresh control circuit in response to the refresh request signal when both the bus access request signals are absent. Thus, the refresh operation can be performed without exerting a harmful influence on the operations of the execution unit and the instruction prefetch circuit. The refresh control circuit may generate a first refresh request signal and a second refresh request signal. The control unit, in this case, generates the refresh grant signal in response to the first refresh request signal only when both the bus access request signals from the execution unit and the instruction prefetch circuit are absent, but generates the refresh grant signal at any time when the second refresh request signal is generated. Thus, the refresh operation can be performed notwithstanding the presence of bus access requests. This refresh control circuit may be adapted to a microprocessor having no instruction prefetch circuit.

REFERENCES:
patent: 4158883 (1979-06-01), Kadona et al.
patent: 4172282 (1979-10-01), Aichelmann, Jr. et al.
patent: 4214305 (1980-07-01), Tokita et al.
patent: 4249247 (1981-02-01), Patel
patent: 4535330 (1985-08-01), Carey et al.
patent: 4625301 (1986-11-01), Berger
"Software/Hardware Approach to Dynamic Memory Refresh", IBM Technical Disclosure Bulletin, vol. 24, No. 10, Mar. 1982.

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