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Microcomputer having a program mode setting circuit

  • US 4,992,937 A
  • Filed: 03/22/1990
  • Issued: 02/12/1991
  • Est. Priority Date: 01/18/1985
  • Status: Expired due to Fees
First Claim
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1. A microcomputer comprising a program memory storing a plurality of instructions for a program, a program counter for accessing said program memory to read an instruction from an address location of said program memory designated by address information of said program counter, a central processing unit executing the instruction read from said program memory, a reset terminal supplied with a reset pulse signal made of a variable width of single pulse, an initialization circuit coupled to said reset terminal and said central processing unit and initializing said central processing unit in response to said reset pulse signal, a pulse width measuring circuit having an input node coupled to said reset terminal and a plurality of output nodes provided in correspondence with different pulse widths of said reset signal, said pulse width measuring circuit measuring the pulse width of said reset pulse signal and producing a selection signal at one of said output nodes in response to the measured pulse width of said reset pulse signal, and an address generating circuit storing a plurality of program start addresses and coupled between each of said output nodes of said pulse width measuring circuit and said program counter, said address generating circuit selectively applying one of said program start addresses to said program counter in response to said selection signal produced at said one of said output nodes, whereby said central processing unit is initialized by the received reset pulse signal and thereafter starts to execute the instructions stored in said program memory from an instruction that is stored in an address location of said program memory designated by the program start address which is applied to said program counter in accordance with the pulse width of said received reset pulse signal.

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