JPS6010349A - Scanning system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a scan method in which a protection function is provided for writing with rewritten data when changing the operating status within a target device using a scan-in/scan-out method.

(2) Prior art and problems In the LSI logic device LG, as shown in FIG.
If the I-FFn is forming a serial scan, other devices can be used to view and possibly change the status of the logical device. That is, external device OT
When a device having a scan memory SCM is brought as R and a scan out SO instruction is given, the states of the flip-flops in the logic device LG are sequentially stored in the scan memory SCM as serial data. If the flip-flop etc. in Fig. 1 is divided into four blocks from the first block IB to the fourth block 4B, Fig. 2A
indicates a case where the status of each block is stored in the scan memo 980M. FIG. 2B shows a case where the flip-flops and the like in FIG. 1 are individually addressed from bit O to bit n, and the individual states are stored as a bit string. The state in scan memory SCM can be rewritten in a predetermined block or bit by appropriately supplying address AD and data DT. When a scan-in SI instruction is given after rewriting, a data string opposite to that described above is applied to the logic device LG, and predetermined items such as flip-flops are set in the rewritten state.

The functions of registers and flip-flops in a logic device differ depending on their setting location, so there are some that do not cause any particular problems even if the set is changed in a lightning situation, some that can only be used for maintenance diagnosis, and some that can only be used for testing. There are things that are possible
Furthermore, some are directly connected to elements that would be destroyed if changed without permission. For example, if a flip-flop that directly controls an internal bus is controlled to cause a bus fight, it becomes a problem. Conventionally, when scanning out a data string, careful attention is paid to the scan memory SCM.
However, since the check function for changed data and addresses is not sufficient, the scan memory could be easily rewritten and scanned in, causing failures.

(3) Purpose of the Invention The purpose of the present invention is to improve the above-mentioned drawbacks and to provide a scanning method that provides a protection function for writing with rewritten data.

(4) Structure of the Invention The structure of the present invention to achieve the above-mentioned object is to read out the logic circuit state inside the target device to the memory of an external device by scanning out, and after rewriting the state of a predetermined address,
In a scanning method that changes the status of a target device by scanning into the target device, the external device is provided with a write mode table for the memory, and the table has a write mode table corresponding to a predetermined address bit, and a mode for rewriting the state of the address bit. A bit is additionally provided to determine whether rewriting is possible, and when the memory rewriting address is applied, the write mode table is referred to, and when rewriting is possible, a write enable signal is sent to the memory.

(5) Embodiment of the invention FIG. 3 is a block diagram showing the configuration of an embodiment of the invention.
The same symbols as in Figure 1 indicate the same things.

WMT indicates a write mode table, and it is assumed that a write enable signal WE is issued to the scan memory during an operation described below. The write mode table WMT contains
A comparison table shown in Figure 4 is provided. FIG. 4A shows a write enable/disable bit for each block when the flip-flops of the logic device LG are divided into blocks. That is, for each block, for example, for the first block, its start address and write permission bin (0 or 1) are provided in contrast.

Data is written to scan memory SMC by a scan out SO instruction. Next, when the rewrite data DT and the rewrite address AD are given, the address is given to the write mode table WMT, the block belonging to the address is known, and whether writing is possible or not can be determined from the corresponding bit. When writing is possible, write enable signal V/E
is given to the scan memory SCM, the address is rewritten with data. Thereafter, the contents of the memory are set in the logical device by a scan-in SI instruction.

Next, FIG. 4B is a diagram showing a case in which the flip-flop of the logic device LG is considered bit by bit, and a write enable/disable bit is provided for each focus. After the data is scanned out, the provision of external data addresses is similar to FIG. 4A.

In the case of FIG. 4B, whether writing is possible or not is determined bit by bit. After the rewriting is completed, the contents of the memory are further set in the logic device.

Note that it is also possible to provide a scan memory/write mode table in the program area and refer to the write mode table by a program.

(6) Effects of the Invention In this manner, with the present invention, it is possible to control writing of scan-out data bit by bit or block by block for a device whose state is to be changed. Therefore, write requests to unspecified areas from the outside can be checked, and requests that may damage the device can be easily eliminated.

[Brief explanation of the drawing]

FIG. 1 is a block diagram illustrating a conventional scan method, FIG. 2 is a diagram showing a data string of the scan memory in FIG. 1, FIG. 3 is a diagram showing the configuration of an embodiment of the present invention, and FIG. The figure is a diagram illustrating the structure of the write mode table in FIG. 3. S CM'-m-Scan memory FF/-Flip-flop WMT-Write mode table WE-Write enable signal Patent applicant Fujitsu Limited Agent Patent attorney Eisuke Suzuki

Claims (1)

[Claims] In the scanning method, the status of the target device is changed by reading out the logic circuit state inside the target device to the memory of an external device by scanning out, rewriting the state of a predetermined address, and then scanning into the target device. A write mode table for the memory is provided, and the table is additionally provided with a bit that corresponds to a predetermined address bit and determines whether the state of the address bit can be rewritten, and when the memory rewrite address is applied, the write mode table A scanning method characterized by sending a write enable signal to the memory when rewritable is possible.