EP0136155A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Single-chip microcomputer comprising means for preventing read-out of its internal ROM
Assignee: Fujitsu Ltd
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Filing: 1984-09-19
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Granted: —
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Expires: 2004-09-19
Abstract
Abstract A single-chip microcomputer 1 connectable to an external memory 8 for expanding its address space, has a first mode of operation in which the available memory region is the region 0000-OFFF of an internal ROM 4 and part of the external memory 8-1, and has a second mode of operation in which the available memory region is the whole of the external memory 8. Such a microcomputer includes inhibiting means 7 for inhibiting the switching from the second mode to the first mode, thereby ensuring that the contents of the internal ROM 4 cannot be read-out.
Inventors
- 👤 Yasuhiro Wakimoto
- 👤 Tetsuo Suzuki
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-28 21:23
CPC Classifications
G; G06; G06F; G06F12/00; G06F12/02; G06F12/06; G06F12/0615; G06F12/0623; G06F12/14; G06F12/1416; G06F12/1425; G06F12/1433; G06F12/0638
Claims Analysis
Total Claims: 6
Claim 1
Independent Claim
128 words
A single-chip microcomputer (1) comprising an internal read-only memory (4), a program counter (3) for generating an address, an interface port (5) connectable to an external memory (8), and a switching means (6) for switching, in response to a switching signal (EA), between a first mode in which both the internal read-only memory (4) and the external memory are used, and a second mode in which only the external memory (8) is used, characterised by an inhibiting means (7) for inhibiting input of the switching signal (EA) into the switching means (6) for switching from the second mode to the first mode when the address output from the program counter indicates an address in an address space other than the address space of the internal read-only memory (4).
Claim 2
Dependent Claim
128 words
A single-chip microcomputer (1) comprising an internal read-only memory (4), a program counter (3) for generating an address, an interface port (5) connectable to an external memory (8), and a switching means (6) for switching, in response to a switching signal (EA), between a first mode in which both the internal read-only memory (4) and the external memory are used, and a second mode in which only the external memory (8) is used, characterised by an inhibiting means (7) for inhibiting input of the switching signal (EA) into the switching means (6) for switching from the second mode to the first mode when the address output from the program counter indicates an address in an address space other than the address space of the internal read-only memory (4).
Claim 3
Dependent Claim
43 words
A single-chip microcomputer according to claim 1, wherein the inhibiting means (7) comprises means for inhibiting the switching signal (EA) from being input into the switching means (6) during a period except for a period during which the program counter (3) is reset.
Claim 4
Dependent Claim
44 words
A single-chip microcomputer according to claim 1 or 2, wherein the inhibiting means (7) comprises means for inhibiting the switching signal (EA) from being input into the switching means 86) when the program counter (3) generates an address for accessing the external memory (8).
Claim 5
Dependent Claim
60 words
A single-chip microcomputer according to any one of the preceding claims, wherein the external memory (8) has a first region (8-1) with a first address space (OFFF-FFFF) different from the address space (0000-OFFF) of the internal read-only memory (4), and having a second region (8-2) with a second address space (0000-OFFF) equal to that of the internal read-only memory (4).
Claim 6
Dependent Claim
47 words
A single-chip microcomputer according to claim 4, wherein the inhibiting means (7) comprises means for inhibiting the switching signal (EA) from being input into the switching means (6) when the program counter (3) generates an address for accessing the first region (8-1) of the external memory (8).
References Cited (Backward Citations)
No citation records indexed.
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