EP0468535A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Microcomputer having ROM data protection function
Assignee: NEC Corp
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Filing: 1991-07-29
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Granted: —
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Expires: 2011-07-29
Abstract
Abstract 5 n7 A single-chip microcomputer includes a program ROM storing a program; a central processing unit executing the program read out from the program ROM for a data processing; an external data input port receiving data to be processed by the central processing means, from an external device; and an external data output port for outputting the data processed by the central processing unit to an external device. The program ROM also stores a test program for testing the program ROM and a plurality of bytes of collation information. The central processing unit has a test mode in which the central processing unit executes the test program, and compares all the plurality of bytes of collation information with a corresponding number of bytes of data sequentially inputted through the external input port, by selecting one of the plurality of bytes of collation information and comparing the selected byte of collation information with one byte of data inputted through the external input port when the selected byte of collation information is selected. Only when all the plurality of bytes of collation information are consistent with all the bytes of data sequentially inputted through the external input port, the central processing unit allowing all contents stored in the program ROM to be outputted through the external output port.
Inventors
- 👤 Hiroshi C/O Nec Corporation Katsuta
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-29 10:28
CPC Classifications
G; G11; G11C; G11C29/00; G11C29/52; G06; G06F; G06F21/00; G06F21/70; G06F21/78; G06F21/79
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
223 words
A microcomputer including a program read only memory storing a program; a central processing means executing said program read out from said program read only memory for a data processing; an external data input means receiving data to be processed by said central processing means, from an external device; and a external data output means for outputting the data processed by said central processing means to a external device; said program read only memory also storing a test program for testing said program read only memory and a plurality of items of collation information, said central processing means having a test mode in which said central processing means executes said test program, and compares all said plurality of items of collation information with a corresponding number of items of data sequentially inputted through said external input means, by selecting one of said plurality of items of collation information and comparing the selected item of collation information with one item of data inputted through said external input means when said selected item of collation information is selected, said central processing means allowing all contents stored in said program read only memory to be outputted through said external output means only when all said plurality of items of collation information are consistent with all the items of data sequentially inputted through said external input means
Claim 2
Dependent Claim
223 words
A microcomputer including a program read only memory storing a program; a central processing means executing said program read out from said program read only memory for a data processing; an external data input means receiving data to be processed by said central processing means, from an external device; and a external data output means for outputting the data processed by said central processing means to a external device; said program read only memory also storing a test program for testing said program read only memory and a plurality of items of collation information, said central processing means having a test mode in which said central processing means executes said test program, and compares all said plurality of items of collation information with a corresponding number of items of data sequentially inputted through said external input means, by selecting one of said plurality of items of collation information and comparing the selected item of collation information with one item of data inputted through said external input means when said selected item of collation information is selected, said central processing means allowing all contents stored in said program read only memory to be outputted through said external output means only when all said plurality of items of collation information are consistent with all the items of data sequentially inputted through said external input means
Claim 3
Dependent Claim
23 words
A microcomputer claimed in Claim 1 wherein said central processing means is brought into said test mode in response to a test signal.
Claim 4
Dependent Claim
149 words
A microcomputer claimed in Claim 1 wherein said program read only memory stores a plurality of bytes of collation information, said central processing means having a test mode in which said central processing means executes said test program, and compares all said plurality of bytes of collation information with a corresponding number of bytes of data sequentially inputted through said external input means, by selecting one of said plurality of bytes of collation information and comparing the selected byte of collation information with one byte of data inputted through said external input means when said selected byte of collation information is selected, said central processing means allowing all contents stored in said program read only memory to be outputted through said external output means only when all said plurality of bytes of collation information are consistent with all the bytes of data sequentially inputted through said external input means
Claim 5
Dependent Claim
92 words
A microcomputer claimed in Claim 1 wherein said program read only memory stores a plurality of items of collation information and a collation information number information, and when said central processing means is brought into said test mode, said collation information number information is set as an internal variable, and each time one of said plurality of items of collation information is compared with one item of data sequentially inputted through said external input means, the internal variable is decremented, so that the comparison is completed when the internal variable becomes zero.
Claim 6
Dependent Claim
50 words
A microcomputer claimed in Claim 4 wherein said plurality of items of collation information are stored at continuous addresses in said program read only memory, so that said plurality of items of collation information are sequentially read out by sequentially incrementing an address supplied to said program read only memory.
Claim 7
Dependent Claim
83 words
A microcomputer claimed in Claim 1 wherein said program read only memory stores a plurality of items of collation information, and one item of interval information, and when said central processing means is brought into said test mode, said interval information is set as an internal variable, and one of said plurality of items of collation information is read out at an interval designated by said interval information, and then compared with one item of data sequentially inputted through said external input means.
Claim 8
Dependent Claim
50 words
A microcomputer claimed in Claim 6 wherein said plurality of items of collation information are stored at continuous addresses in said program read only memory, so that said plurality of items of collation information are sequentially read out by sequentially incrementing an address supplied to said program read only memory.
References Cited (Backward Citations)
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