Circuit for testing circuit blocks controlled by microinstructions

Abstract: A test circuit for testing circuit blocks of an integrated circuit device controlled with microinstructions comprising a microinstruction register (13). The microinstruction register (13) is basically the one originally provided in the integrated circuit device but it holds not only a microinstruction read out of a micro-ROM (12) but also a control signal that is set externally to set the circuit blocks of the integrated circuit device. The control signal set externally in the microinstruction register (13) is decoded by a microdecoder (14) to test operation of the circuit blocks.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a test circuit for testing operation of a circuit device comprising circuit blocks that are controlled by microinstructions. Description of the Prior Art In a microprocessor, circuit blocks such as ALUs (Arithmetic Logic Units), shifters and register files are connected to each other through an internal bus and controlled with microinstructions. To efficiently test operation of those circuit blocks from the outside of an LSI chip that contains the circuit blocks, a test circuit such as the one shown in Fig. 1 is conventionally used. In Fig. 1, a macroblock 1 is a circuit block such as an ALU and a shifter that receives data from an internal bus 2 of a microprocessor via latch circuits 3 (LAT1 and LAT2). A macroblock 4 such as a register file directly receives data from the internal bus 2. Signals of the macroblocks 1 and 4 are outputted to the internal bus 2 via output buffers 5. The internal bus 2 is connected to a data pin 7 and an address pin 8 through I/O buffers 6. Data are inputted to and outputted from the circuit blocks 1 and 4 via the pins 7 and 8. The macroblocks 1 and 4 are connected to circuits 9 (hereinafter called the TFF circuits). As will be explained later with reference to an equation, the TFF circuits 9 receive, under a normal mode, control signals from a control circuit previously assembled in the chip and provide the control signals to the macroblocks to let the macroblocks execute predetermined operations. Under a test mode, the TFF circuits 9 receive control signals from the outside of the chip and provide the control signals to the macroblocks to let the macroblocks execute operations to be tested. The latch circuits 3 of the macroblock 1, the macroblock 4, the output buffers 5 of the macroblocks 1 and 4 and the I/O buffers 6 are connected to circuits 10 and enabled or disabled by the circuits 10, respectively. The circuit 10 is constituted similar to the circuit 9 and, therefore, it is also called the TFF circuit. An output of each of the TFF circuits 9 and 10 is determined according to the following equation in which the TFF circuits 9 and 10 are generally distinguished from each other with the use of a subscript "i" (or "j"): (OUTPUT)i = MBT * SGN + MBT * ENi * Qi In the expression, the MBT is an operation mode selection signal. When the signal MBT is 0, a normal mode is selected. When the signal MBT is 1, a test mode is selected. The SGN is a control signal for the normal mode. The ENi are enable signals for the respective TFF circuits 9 and 10 are generated by an enable signal generating circuit (TGEN) 11. The enable signal generating circuit 11 receives a sequence control signal TEN that controls a test sequence. The enable signals ENi to the TFF circuits are not necessarily different from each other. Depending on operations necessary for the test, a common enable signal may be used for a plurality of the TFF circuits. The Qi are outputs of flip-flop circuits (EFFs) arranged in the TFF circuits 9 and 10. The flip flop circuits of the TFF circuits 9 and 10 are arranged to form a series scan chain. A Q-output of each of the flip-flop circuits is set to 0 or 1 in synchronism with a clock. When the signal MBT changes from 0 to 1, a logical value held at the Q-output at the time of this change of signal MBT is kept as it is while the signal MBT is maintained at 1. If the signal ENi is applied to the TFF circuit 10(i) during a test period (with the Q-outputs of respective flip-flops having been set and with the signal MBT being 1) and if a signal Qi (fixed) of the flip-flop circuit of the TFF circuit 10(i) is 1, a circuit connected to the TFF circuit in question is enabled. If a signal ENi is applied to the TFF circuit 9(j) of the macroblocks 1 and 4, a control signal held in the TFF circuit 9(j) is applied to the macroblocks 1 and 4. With the arrangement mentioned in the above, external data can be inputted to the macroblocks 1 and 4, and data can be read out of the macroblocks 1 and 4 to the outside to directly test operation of the macroblocks 1 and 4. However, the conventional test circuit of this sort has problems. For inputting control signals to the respective macroblocks, the TFF circuits shall be arranged for the macroblocks, respectively. This may require particular areas and wiring. Therefore, it is quite disadvantageous to install the conventional test circuit in an integrated circuit. Moreover, it is impossible to test the macroblocks under operating conditions that are completely the same as actual operating conditions realized by control signals issued by a microdecoder. SUMMARY OF THE INVENTION An object of the present invention is to provide a circuit device comprising a test circuit having simpler structure and easy to install in the circuit. Another object of the present invention is to provide a circuit device comprising a test circuit that can control operation of respective macroblocks according to signals decoded by a microdecoder, similar to actual operation. The above objects are achieved by providing in a circuit device a test circuit of the invention comprising a microinstruction register and masking means according to claim 1. Advantageous embodiments are described in the subclaims These and other objects, features and advantages of the present invention will be more apparent from the following detailed description of preferred embodiments in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a view explaining a conventional test circuit; Fig. 2 is a block diagram showing a test circuit according to an embodiment of the invention; and Fig. 3 is a timing chart showing operations of reading external data, operating the data in a macroblock 1, storing a result of the operation in a macroblock 4 and outputting the result outside. DETAILED DESCRIPTION OF THE EMBODIMENTS A test circuit according to an embodiment of the invention will be explained. Similar to the circuit shown in Fig. 1, a test circuit shown in Fig. 2 tests macroblocks such as ALUs and register files of a microprocessor. In Fig. 2, circuit elements similar to those shown in Fig. 1 are represented with like numerals. In Fig. 2, the microprocessor has a micro-ROM 12, a microinstruction register (MIR) 13 and a microdecoder 14. The micro-ROM 12 is a read only memory for storing microinstructions that control the macroblocks. The microinstruction register (MIR) 13 is a register in which a microinstruction read out of the micro-ROM 12 is set. According to the invention, the microinstruction register (MIR)) 13 is so constituted that a microinstruction for controlling operation of the macroblocks is externally set in the MIR 13. In this embodiment, the microinstruction register (MIR) 13 comprises flip-flops (FFs) connected in series to form a scan chain. Control signals are sequentially inputted from a scan input terminal of the scan chain and set in the flip-flops. Similar to the TFF circuit 10, each bit of the microinstruction register (MIR) 13 holds a logical value that exists when the signal MBT changes from 0 to 1, during a period in which the signal MBT is maintained at 1 after it is changed from 0 to 1. However, while the signal MBT is being 0, a scan operation mode under which a microinstruction is set from the outside shall be distinguished from a normal mode under which the contents of the micro-ROM are stored. The microdecoder 14 decodes a microinstruction set in the microinstruction register (MIR) 13. An output of the microdecoder 14 is sent to the macroblocks 1 and 4 to control operation of the macroblocks 1 and 4. The masking circuit 15 validates or invalidates (enables or disables) a signal to be sent from the microinstruction register (MIR) 13 to the microdecoder 14. To validate the signal, the signal outputted from the MIR 13 may be inputted as it is to the microdecoder 14. To invalidate the signal, a microinstruction such as a NOP instruction (NO OPERATION instruction) having no effects on the control of the macroblocks to be tested is applied to the microdecoder 14 irrespective of the contents of the microinstruction register (MIR) 13. The masking signal generating circuit 16 generates the masking signal according to a test sequence control signal (TEN) that is given externally. To operate the macroblocks 1 and 4 in a test sequence, the masking signal from the masking signal generating circuit 16 becomes inactive. Then, the control signal set in the microinstruction register (MIR) 13 is decoded by the microdecoder 14. Similar to updating an output of the microinstruction register (MIR) 13, the masking signal is activated and inactivated in synchronism with clocks. Generally, the masking signal switches the validation and invalidation of the output of the MIR 13 at timing that is delayed little behind the timing of updating the MIR 13 under the normal mode. This delay may be reduced to an extent of practical negligence through circuitry devices. Accordingly, including a decoding time of microinstruction (control signal) under the normal mode, an operation speed of macroblocks installed in an LSI can correctly be evaluated. An example of test sequence will be explained with reference to a timing chart of Fig. 3. In this example, the test circuit according to the embodiment puts external data in the macroblock (ALU) 1 to operate the data in the macroblock 1. A result of the operation is once stored in the macroblock (register file) 4. Then, the test circuit outputs the stored result to the outside. Enable signals ENi (each corresponding to one of RE1, RE2, RE3, WE1, WE2) shown in Fig. 3 are given to TFF circuits 10. These enable signals ENi are generated in an enable signal generating circuit (TGEN) 11 by simply combining signals TEN1, TEN2, and TEN3. Based on a sequence control signal TEN applied to the enable signal generating circuit 11, flip-flops connected in series in the enable signal generating circuit 11 generate and output the signals TEN1, TEN2 and TEN3. Firstly, the scan operation mode is set with the signal MBT being 0 and with the microinstruction register (MIR) 13 being under a scan operation status, and a microinstruction for specifying operation of the macroblocks 1 and 4 is inputted from the scan input terminal and set in the microinstruction register (MIR) 13. To enable the latch circuits 3 and output buffers 5 of the macroblock 1, the macroblock 4 and the output buffers 5 of the macroblock 4, the TFF circuits 10 for controlling them are set. After that, the signal MBT is set to 1, and the signal TEN shown in Fig. 3 is applied. With the enable signal TEN1 of 1, data D1 is applied to a data pin 7. Then, the data D1 is inputted in an internal bus 2 via an I/O buffer 6. At this time, the enable signal WE1 become 1, and the data D1 on the internal bus 2 is put in the latch circuit (LAT1) 3. After that, data D2 is applied to the data pin 7. The enable signal TEN1 is kept to be 0 in the next cycle so that the data D2 is inputted to the internal bus 2. Also in this cycle, the enable signal WE2 becomes 1 so that the data D2 is taken in the latch circuit (LAT2) 3. During the read of the data D1 and D2, the masking signal is kept to be 1 so that microinstruction in the microinstruction register (MIR) 13 may be inhibited from being decoded. After the data D1 and D2 have been read, the masking signal become 0. Then, the microinstruction in the microinstruction register (MIR) 13 is decoded by the microinstruction decoder 14 to provide a control signal that is applied to the macroblock 1. Then, the data D1 and D2 in the latch circuits 3 are operated in the macroblock 1. At the same time, the signal RE1 become 1 so that the output buffers 5 of the macroblock 1 and the macroblock (register file) 4 are enabled. A result of the operation in the macroblock 1 is stored in the macroblock 4 via the internal bus 2. After that, the enable signal RE2 becomes 1 so that the statuses of flags of the operation stored in a flag register 17 are read from the pin 8 via the output buffers 5, internal bus 2 and I/O buffers 6. Further, the enable signal RE3 becomes 1 so that the operation result (data portion) of the macroblock 1 stored in the macroblock 4 may be read outside from the pin 7 or 8 via the buffers 5, internal bus 2 and buffers 6. With the signal MBT=1, a series of test sequences involving the data write from the outside, operation in the macroblock 1 and operation result (including flags) read to the outside may be repeated with the use of different data (D1′ and D2′) to carry out necessary tests on the macroblock 1 precisely at high speed. As described in the above, according to the test circuit of the invention, a microinstruction is externally set in the microinstruction register (MIR), and the control signal is decoded by the microdecoder to test operation of the macroblocks. Therefore, without interposing complicated control logic for converting machine language instructions into microinstructions, the circuit blocks controlled by microinstructions can directly be tested. Since the microinstruction register (MIR) and microdecoder that are originally provided for a microprocessor are used to set a microinstruction in the MIR and decode the microinstruction in the microdecoder to provide a control signal for the macroblocks, the TFF circuits for applying control signals to macroblocks of the conventional test circuit are not required in the invention. Therefore, the test circuit of the invention has simpler structure and is easily installed in an integrated circuit. If necessary control data are once set in TFF circuits and in the microinstruction register (MIR) and if the test mode signal MBT is once set to 1, the test sequence control signal TEN is changed according to predetermined timing to repeatedly apply different data. Then, substantially under the same conditions as those in the normal mode in which a microinstruction set in the microinstruction register (MIR) is decoded by the microdecoder to control operation of the macroblocks, the operation of the macroblocks can be tested with accuracy as required and at high speed.

Claims: A integrated circuit device comprising circuit blocks (1,4) controlled with microinstructions; a micro-ROM (12) for storing said microinstructions; a microdecoder (14) for decoding said microinstructions; input/output means (5,6,7,8) for inputting and outputting data to and from the circuit blocks; a test circuit comprising a microinstruction register (13) for holding a test microinstruction which is supplied externally and set in the microinstruction register for testing the circuit blocks; and masking means (15) for enabling and disabling the decoding of the microinstruction held in said microinstruction register (13); and control means (11,16) for controlling the test data input and test data output operation through said input/output means and for controlling the operation of said masking means (15) according to control signals externally supplied during testing the circuit blocks, wherein a microinstruction for testing externally set in said microinstruction register is decoded to test the operation of said circuit blocks. A circuit device according to claim 1, wherein said microinstruction register comprises flip-flop circuits connected in series to form a scan chain having an input terminal to which said microinstrucitions for testing are externally supplied. A ciruit device according to any one of claims 1 and 2, further comprising masking signal generating means (16) for generating a masking signal according to a test sequence signal inputted externally to control said masking means (15) with the masking signal. A circuit device according to any one of claims 1 to 3, further comprising enabling/disabling signal generating means (10) for generating signals for enabling and disabling the circuits blocks (1,4) to be tested and circuit elements (3,5) related to the operation of said circuit blocks to be tested. A circuit device according to claim 4, wherein said enabling/disabling signal generating means comprise flip-flop circuits (10) connected in series to form a scan chain.

Inventors: NOZUYAMA YASUYUKI, NOZUYAMA, YASUYUKI
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1989
Main classification: G06F11
IPC codes: G06F11