JPH0420879A - Boundary scanning circuit - Google Patents

Abstract

PURPOSE:To simplify a circuit and to improve reliability by passing signals in both directions, as well as a scanning signal, through the same FF with an integrated circuit and the like. CONSTITUTION:At first, signals for switching-control-signal terminals 12 and 13 in normal operation are '1' and '0'. The direction of the signal is determined by a signal for a signal-direction switching-control-signal terminal 17. In boundary scanning operation, the signals for the terminals 12 and 13 become '0' and '1'. The signal for the direction switching terminal 17 has no relation. At this time, the scanning data are inputted through a terminal 14. The data are made to pass through an FF 18 and outputted to a scanning signal terminal 16. By using one FF in this way, the signals in both directions and the scanning circuit in the single direction can be constituted, and the reliability can be improved.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention is an integrated circuit (hereinafter referred to as IC) used in information communication equipment such as satellite communication and mobile communication equipment, and home appliances such as televisions and VTRs. The present invention relates to a boundary scan circuit used for confirming the mounting state of an IC.

Conventional technology Boundary scan circuits have been considered for use in diagnosing the state of wiring in precision equipment and electronic equipment that requires high reliability, including satellite communications and mobile communications. In many cases, a configuration using a frimbfromp circuit has been considered. Recently, integrated circuit technology has progressed and more circuits can be integrated, and it has become necessary to improve the reliability of equipment, so it is considered that it can be widely used as a self-diagnosis circuit. It is being However, in implementing these methods, the scanning circuit and control circuit for bidirectional signal directions become complicated, making it difficult to put them into practical use. The configuration of a conventional boundary scan circuit will be described below with reference to the drawings.

FIG. 2 is a conceptual diagram of a boundary scan circuit. 21 and 22 of the same figure are respectively No. 1. 2nd IC1 same figure 21a
-d, 22a-d are each element of a boundary scan circuit (hereinafter simply referred to as a boundary scan circuit), 23a-d are mounting lines between ICs, and dotted lines 24 are data bits during a boundary scan test. represents the direction of movement. In reality, there is a line connected in this direction, and it is called Scanhas. In normal circuit operation, signals between the ICs are transmitted through the lines shown in FIG. 23, but during a boundary scan test, data bits are sent from the control circuit in the direction of the dotted arrow in FIG. 24. Here, the boundary scan method will be explained as follows. First, the boundary scan data bits are sent in the direction of the arrow using a clock signal, and when the first data focus reaches the final boundary scan circuit, the scan direction is switched to the normal direction (switching between data bus and scan bus). ), each data bit is transferred only once in their data direction. Then, the scanning direction is switched again and scanning is continued until the final scan data bit is output from 22d in FIG. This input data bit is predetermined information, and since the information that has finally passed through all the boundary scan circuits is known, it is possible to diagnose whether each mounted wiring path is correctly connected. FIG. 3 is a specific circuit diagram of the boundary scan circuit of FIG. 2. In the same figure, 31 and 37 are the input and output of IC signals during normal operation, and 37 in the same figure is the element 37a.
It becomes a connection line (corresponding to the connection line 23 in FIG. 2) with other ICs through the . 32 and 33 in the same figure are a pair of control signals that switch between normal operation and boundary scan.
33 in the figure is an inverted signal of 32. Figure 34.3
Reference numeral 6 indicates input and output signal terminals for data bits during boundary scanning, and 38 in the same figure indicates terminals for shifting scan data one by one during boundary scanning by utilizing signal accumulation. 35 is necessary for operating the flip-flop circuit 38 and passing the signal, and the long signal 39 is an input terminal of the logic circuit. In the case of normal operation, the control signals shown at 32 and 33 in FIG. 3 become "1" and "0", respectively, and the signals in the IC are outputted from FIG. 31 through the flip-flop 38 to 37 in FIG. In the case of boundary scan, the control signals are rQ and rl, respectively, and data pins from other scan circuits are input from 34 in the same figure, pass through the flip-flop 3B like the above signal, and are output from 36 in the same figure. be done.

In this way, each input/output terminal can be switched by a control signal, and data can be accumulated by passing it through a flip-flop circuit, so that the operation described in FIG. 2 can be performed. This circuit is an example of a circuit used for unidirectional signals. FIG. 4 is an example of a boundary scan circuit used for bidirectional signals. This diagram is constructed using two of the circuits shown in FIG. 3 above. Figure 41r and I are bidirectional signal terminals, Figure 4
2.43 is a control signal for switching between normal operation and boundary scan operation; 44r and 441 in the same figure are input/output terminals for data signals during boundary scan operation; 45 in the same figure is an input terminal for a long signal for flip-flop; 46 is an output terminal for scan data, 47 in the same figure is an input terminal for a control signal for switching the direction of the signal, and 48 in the same figure is a flip-flop. By these signals, during normal operation, the input of the control signal 47 causes the signal to shift to the right (41r) when r('').
When the signal is rQ, the signal is sent from the left (411) to the left (411), and from the left to the right when the signal is rQ. On the other hand, in the case of boundary scan, the control signals 42 and 43 are "OJ 'i
Then, the switch 49 inside the circuit is turned off. Then, the direction of the boundary scan is switched by the direction switching control signal 47, the inputs 44r and I are selected, and the inputs 44r and I are output to the scan data output terminal 46. In the case of the same figure, when the direction control signal 47 is "IJ", the signal 441 is sent to the output 46,
"44r signal is output during OJ. This section is also an example of a bidirectional boundary scan circuit, and depending on its control method, there is also a circuit that has one skid output for each direction. In addition, 50a ~50d is a logic circuit for each signal, 50e
, 50f is a 35tate element, and 48b is a flip-flop.

Problems to be Solved by the Invention However, in the configuration of the bidirectional boundary scan circuit as described above, the flip-flops that the signal or scan data passes through differ depending on the direction, so when one of the flip-flops fails, which one The addition of this circuit has the problem of reliability problems, such as making it difficult to tell when a flip-flop has failed and complicating the control method and circuitry.

The present invention is intended to solve the above problems, and the first purpose is to reduce the number of components that make up the circuit by reducing the number of components that make up the circuit by reducing the number of clip-flops through which bidirectional signals and scan data pass, thereby improving reliability. be. The second purpose is to simplify the control method and circuit. The third purpose is to make it easier to find the location of a failure when it occurs.

Means for Solving the Problems In order to achieve the above object, the technical solution of the present invention is as follows:
First, the clip-flops through which signals and scan data pass are made into one and the same clip-flop, thereby simplifying the peripheral control circuits. Secondly, the scanning direction during boundary scanning can be operated in a single direction.

Effects of the present invention With the above configuration, firstly, both the signal and the scan data pass through the same flip-flop, so that the signal can operate in both directions, and secondly, during boundary scan, the scan data passes through the same flip-flop. It is designed so that it passes only once and is unidirectional.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to FIG. FIG. 1 is a circuit diagram of a boundary scan circuit according to the present invention. In Figure 1, 11r and 111 are signal input/output terminals, 12.13 in the same figure is a control signal terminal for switching between normal operation and boundary scan, and 14.1 in the same figure.
Reference numerals 6 designate scan data input and output signal terminals, 15 in the same figure a clock signal input terminal, 17 in the same figure a control signal input terminal for switching the signal direction, and 18 in the same figure a clip-flop. 19a to 19g are logic circuits for each signal,
20a20b is a 35tate element.

The operation of the above configuration will be explained below.

First, during normal operation, the signals to the control signal terminals 12 and 13 are rl and r□, respectively, and the direction of the signal is determined by the signal to the signal direction switching control signal terminal 17. In the figure, when the signal is "1", the signal goes from the right (11r) to the left (111), and when it is "0", the signal goes from the right (11r) to the left (111), and vice versa, and in both cases, the signal passes through the same clip-flop 18. Next, during the boundary scan operation, the signal to the control signal terminals 12 and 13 is rO.

It becomes "1", and the signal to the direction switching control signal terminal 17 becomes irrelevant. In other words, it will be ignored. At this time, scan data is input from the terminal 14, passes through the flip-flop 18, and is output to the terminal 16 in FIG. Note that when switching between the scan canvas and the signal line, the signal to the control signal input terminal 17 is set to "1".
If it is set to either "0" or "0", the direction of the scan data is determined and the connection line can be checked.

As is clear from the above description, according to this embodiment, a bidirectional signal and unidirectional scan circuit can be configured with a simple circuit configuration using one flip-flop.
It is possible to improve reliability and simplify control.

In the above description, a D-type clip-flop was used, but a circuit element capable of accumulating other signals may be used.

Effects of the Invention As described above, the present invention allows both bidirectional signals and scan signals to pass through the same clip-flop, thereby simplifying the circuit and improving reliability. Furthermore, the direction of data bits during boundary scanning can be defined, which has great effects, such as simplifying IC design and control methods when used.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a boundary scan circuit according to an embodiment of the present invention, Fig. 2 is a conceptual diagram of the operation of a conventional boundary scan method, and Fig. 3 is a circuit diagram of a conventional unidirectional boundary scan circuit. , FIG. 4 is a circuit diagram of a conventional boundary scan circuit connected to a bidirectional signal line. 11... Input/output terminal, 12.13...
Switching control signal, 14.16...Scan signal terminal, 15...Clock signal terminal, 17...
...Switching control signal input terminal, 18...
flip flop. Name of agent: Patent attorney Shigetaka Awano

Claims (2)

[Claims] (1) A boundary scan circuit that is an integrated circuit or the like and has a control circuit that passes through the same flip-flop circuit in both directions. (2) A boundary scan circuit having, in place of the bidirectional boundary scan circuit according to claim 1, a control circuit that switches between a check state and a normal state, and checks both directions in one direction.