JPH05108527A - Input/output circuit for microcomputer - Google Patents

Abstract

PURPOSE:To reduce the number of ports at a microcomputer for connecting an input/output equipment by switching a port for sharing inputting/outputting to be used as the input port and the output port to an input operation and an output operation while sharing time. CONSTITUTION:First and second select signal terminals S1 and S2 are connected to the bases of two transistors TR 1 and TR 2, and the collectors of these transistors are connected to a power supply terminal VDD of a microcomputer 1. Between the emitters of the two transistors TR 1 and TR 2 and four shared ports 101-104, eight LED LE1-LE 8 are respectively connected through resistors 3. Among the power supply terminal VDD of the microcomputer 1, the first and second select signal terminals S1 and S2 and the shared ports 101-104, resistors 4 are connected. Since four select signals S1, S2, T1 and T2 are switched to an H level and an L level while sharing time in this input/output circuit, the shared ports 101-104 are switched to the input operation and the output operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an input / output circuit of a microcomputer (microcomputer) connected to a plurality of input devices such as switches and a plurality of output devices such as LEDs (light emitting diodes).

[0002]

2. Description of the Related Art FIG. 3 shows an example of a conventional microcomputer input / output circuit.

In FIG. 3, a microcomputer (1) is connected to eight switches (SW1) to (SW8) which are input devices and eight LEDs (LE1) to (LE8) which are output devices. The microcomputer (1) is provided with four input ports (I1) to (I4) and four output ports (O1) to (O4), and two select signal terminals (S1) (S2) of the microcomputer (1). ), Select signals S1 and S2 are output respectively.

Between the four input ports (I1)-(I4) and the two select signal terminals (S1) (S2), eight switches (SW1)-
Each (SW8) is connected via a diode (2). The two select signal terminals (S1) (S2) are connected to the bases of the two transistors (TR1) (TR2), and the collectors of these transistors (TR1) (TR2) are the power supply terminals (VDD) of the microcomputer (1). It is connected to the. Also, the emitters of the two transistors (TR1) (TR2) and the four output ports (O1) to (O
Between 4), 8 LEDs (LE1) to (LE8) have resistance.
Connected via (3). A resistor (4) is connected between the power supply terminal (VDD) of the microcomputer (1), the select signal terminals (S1) (S2), and the input ports (I1) to (I4).

One of the two select signals S1 and S2 is H.
(High) level and the other is switched to L (Low) level. The four input ports (I1) to (I4) always output H level, and the two output ports (O1) to (O4)
Are switched to H level and L level, respectively.

When the first select signal S1 is at L level, the first switch (SW1) is at the first input port (I1), the third switch (SW3) is at the second input port (I2), and the third input port (I3). ) Is the 5th switch (SW5) and the 4th input port (I4) is the 7th switch
The status of (SW7) is read. First input port (I
Since 1) always outputs H level, when the first select signal S1 is H level, the first input port (SW1) is open or closed. I1) remains at H level, and therefore the first switch (SW
The status of 1) cannot be read. In contrast, the first
When the select signal (S1) is at L level, the first switch (S
If W1) is in the open state, the first input port (I1) remains at the H level, but if the first switch (SW1) is in the closed state, the first input port (I1) is at the L level, so , First
The status of the switch (SW1) can be read. The same applies to the third, fifth and seventh switches (SW3) (SW5) (SW7).

Similarly, when the second select signal (S2) is at L level, the second switch (SW2) is at the first input port (I1), the fourth switch (SW4) is at the second input port (I2), The state of the sixth switch (SW6) is read at the 3rd input port (I3), and the state of the 8th switch (SW8) is read at the 4th input port (I4).

When the first transistor (TR1) is on and the first output port (O1) is at L level, the first LED (LE1)
Lights up. If the first transistor (TR1) is off,
The first LED (LE1) is not energized and therefore the first LED
(LE1) is off. Even if the first transistor (TR1) is turned on, if the first output port (O1) is at H level,
Again, the first LED (LE1) is not energized, so
LED (LE1) is off. When the first transistor (TR1) is turned on and the first output port (O1) is at L level, the first LED (LE1) is energized, and therefore,
The first LED (LE1) lights up.

Similarly, when the first transistor (TR1) is on, if the second output port (O2) is at L level, the second LE
If D (LE2) is the L level of the third output port (O3), the third LED (LE3) is lit, and if the fourth output port (O4) is the L level, the fourth LED (LE4) is lit. Also, the second
When the transistor (TR2) is on, the first output port (O1)
Is the L level, the fifth LED (LE5) is the sixth LED (LE6) when the second output port (O2) is the L level, and the seventh LED (LE7) is the third output port (O3) is the L level. ) But,
If the eighth output port (O8) is at L level, the eighth LED (LE
8) lights up respectively.

Next, an example of the operation of this input / output circuit is shown in FIG.
The timing chart will be described.

During the period from time t1 to t5, the first select signal S1
Is at H level and the second select signal S2 is at L level, the second switch (SW2) is at the first input port (I1), the fourth switch (SW4) is at the second input port (I2), and the third switch is at the third level. The sixth switch (SW6) is read at the input port (I3), and the eighth switch (SW8) is read at the fourth input port (I4). Further, during this period, the first transistor (TR1) is on and the second transistor (TR2) is off. Of these, time t1
From 1 to t2, the first output port (O1) is at L level,
Since the fourth output ports (O2) to (O4) are at the H level, only the first LED (LE1) lights up. From time t2 to t3, the second output port (O2) is at L level and the first, third and fourth output ports (O1) (O3) (O4) are at H level, so the second LED ( Only LE2) lights up. Time t3 to t4
During this period, the third output port (O3) is at the L level, and the first, second and fourth output ports (O1) (O2) (O4) are at the H level, so only the third LED (LE3) is Light. From time t4
During t5, the fourth output port (O4) is at L level, and the first to third
Since the output ports (O1) (O2) (O3) are at H level,
Only the 4th LED (LE4) lights up.

During the period from time t5 to t9, the first select signal S1
Is at the L level and the second select signal S2 is at the H level, the first switch (SW1) is at the first input port (I1), the third switch (SW3) is at the second input port (I2), and the third switch is at the third level. Reading of the fifth switch (SW5) is performed at the input port (I3), and reading of the seventh switch (SW7) is performed at the fourth input port (I4). Further, during this period, the first transistor (TR1) is off and the second transistor (TR2) is on. Of these, time t5
From 1 to t6, the first output port (O1) is at L level,
Since the fourth output ports (O2) to (O4) are at the H level, only the fifth LED (LE5) lights up. From time t6 to t7, the second output port (O2) is at L level and the first, third and fourth output ports (O1) (O3) (O4) are at H level, so the sixth LED ( Only LE6) lights up. Time t7 to t8
During this period, the third output port (O3) is at L level, and the first, second and fourth output ports (O1) (O2) (O4) are at H level, so only the seventh LED (LE7) is Light. From time t8
During t9, the fourth output port (O4) is at L level, and the first to third
Since the output ports (O1) (O2) (O3) are at H level,
Only the 8th LED (LE8) lights up.

[0013]

In the above-mentioned conventional input / output circuit of the microcomputer, the maximum number of input devices is the product of the number of select signals and the number of input ports, and the number of select signals and the number of output ports. Although the number of output devices equal to the product of and can be used, an input port and an output port are required separately, and the number of ports of the microcomputer may become insufficient due to the increase in the number of input devices and output devices.

The object of the present invention is to solve the above problems,
It is to provide a microcomputer input / output circuit that requires a small number of microcomputer ports.

[0015]

An input / output circuit of a microcomputer according to the present invention is an input / output circuit of a microcomputer connected to a plurality of input devices and output devices, and has a dual input / output function. A port is provided, and this input / output port can be switched to an input operation and an output operation in a time division manner.

[0016]

Since the I / O port is switched to the input operation and the output operation in a time division manner, the input operation and the output operation can be performed by one I / O port.

[0017]

Embodiments of the present invention will be described below with reference to FIGS.

FIG. 1 shows an example of the input / output circuit of the microcomputer (1), and the same parts as those in the conventional example of FIG. 3 are designated by the same reference numerals.

In FIG. 1, the microcomputer (1) has eight switches (SW1) to (SW8) and eight LEs as in the case of FIG.
It is connected to D (LE1) to (LE8). Also, the microcomputer
(1) has four I / O ports (IO1) to (IO4) and four select signal terminals (S1) (S2) (T1) (T2)
The select signals S1, S2, T1 and T2 are respectively output from the.

Eight switches (SW1) to (SW8) respectively connect the diode (2) between the four dual-purpose ports (IO1) to (IO4) and the third and fourth select signal terminals (T1) and (T2). Connected through. First and second select signal terminals (S1)
(S2) is connected to the bases of the two transistors (TR1) (TR2), and the collectors of these transistors (TR1) (TR2) are connected to the power supply terminal (VDD) of the microcomputer (1).
Also, between the emitters of the two transistors (TR1) (TR2) and the four dual-purpose ports (IO1) to (IO4), 8 LEDs (LE
1) to (LE8) are connected via a resistor (3). In addition, the power supply terminal (VDD) of the microcomputer (1), the first and second select signal terminals (S1) (S2), and the dual-purpose port (IO
A resistor (4) is connected between 1) and (IO4).

In this input / output circuit, four select signals
By switching S1, S2, T1, and T2 between H level and L level in a time division manner as follows, four dual-purpose ports (IO1) to (I
O4) is switched between input operation and output operation.

When performing the input operation, both the first and second select signals S1 and S2 are switched to the L level. Further, one of the third and fourth select signals T1 and T2 is switched to the H level and the other is switched to the L level. In this state, the required dual-purpose ports (IO1) to (IO4) are switched to the H level, and the dual-purpose ports (IO1) that are at the H level
~ (IO4) and its dual-purpose ports (IO1) to (IO4) and L
The states of the switches (SW1) to (SW8) corresponding to the select signals T1 and T2 that are at the level are read. When both the first and second select signals S1 and S2 are switched to the L level, the two transistors (TR1) and (TR2) are both off, and therefore the dual-purpose ports (IO1) to (IO4)
Is set to H level or L level, whichever L
ED (LE1) to (LE8) also do not light. That is, in this case, the output operation cannot be performed. In such a state, the third select signal T3 is at L level and the fourth select signal is
T4 is switched to H level, and the first dual-purpose port (IO
If 1) is switched to H level, this port (IO1)
The state of the first switch (SW1) is read with. If the fourth select signal T4 is at the H level, the first dual-purpose port (IO) can be set whether the second switch (SW2) is open or closed.
The state of 1) does not change, so the second switch (SW2)
Can not read the state of. Third select signal T3
Is at the L level, the first combined port (IO1) remains at the H level when the first switch (SW1) is in the open state.
If the first switch (SW1) is closed, the first combined port (I
O1) becomes L level, and therefore the first switch (SW
The status of 1) can be read. Similarly, while the third select signal T3 is switched to L level and the fourth select signal T4 is switched to H level, if the second combined port (IO2) is switched to H level, this port (IO2) If the state of the third switch (SW3) is such that the third combined port (IO3) has been switched to the H level, this port (IO3) causes the fifth switch
If the status of (SW5) is such that the fourth combined port (IO4) has been switched to the H level, the seventh switch (SW4)
The state of 7) is read respectively. Further, when the third select signal T3 is switched to the H level and the fourth select signal T4 is switched to the L level, if the first combined port (IO2) is switched to the H level, the second port at this port (IO1) switch
If the status of (SW2) is such that the second combined port (IO2) is switched to H level, this port (IO2) will cause the fourth switch (SW2)
In the state of 4), if the third combined port (IO3) is switched to the H level, the sixth switch (SW6) will be used at this port (IO3).
If the fourth combined port (IO4) is switched to the H level, the state of the eighth switch (SW8) is read by this port (IO4).

When performing the output operation, both the third and fourth select signals are switched to the H level. Further, at least one of the first and second select signals S1 and S2 is switched to the L level. Then, in such a state, the dual-purpose ports (IO1) to (IO4) are set to H level or L level.
By switching to the level, the dual-purpose port (IO1) ~
The LEDs (LE1) to (LE8) corresponding to (IO4) and the select signals S1 and S2 that are at the L level are switched off or on. When the third and fourth select signals T3 and T4 are both switched to the H level, the switches (SW1) to (S
Whether the W8) is open or closed, the dual-purpose port (I
The states of (O1) to (IO4) do not change, and
The status of (SW1) to (SW8) cannot be read. That is, in this case, the input operation cannot be performed. In this state, when the first select signal S1 is switched to H level, if the first combined port (IO1) is at H level, the first LED (LE1) is turned off and the first combined port (IO1)
If the L-level is, the first LED (LE1) is lit, if the second I / O port (IO2) is H-level, the second LED (LE2) is off, and if the second I / O port (IO2) is L-level, 2L
ED (LE2) lights up, if the third combined port (IO3) is at H level, the third LED (LE3) goes off, and the third combined port (IO
If 3) is at L level, the third LED (LE3) is lit, and if 4th combined port (IO4) is at H level, the fourth LED (LE3) is
4) goes off, and if the fourth combined port (IO4) is at L level, the fourth LED (LE4) goes on. Similarly, when the second select signal S2 is switched to H level, the fifth LED (LE5) is turned off if the first combined port (IO1) is at H level.
If the first combined port (IO1) is at L level, the fifth LED (L
E5) lights up, and if the second combined port (IO2) is at H level, the sixth LED (LE6) goes off, and the second combined port (IO2) goes to L.
If the level is 6th LED (LE6) is on, if the third combined port (IO3) is H level, then the 7th LED (LE7) is off, if the 3rd combined port (IO3) is L level, it is the 7th LE.
D (LE7) lights up, if the fourth combined port (IO4) is at H level, the eighth LED (LE8) goes off, fourth combined port (IO4)
If is the L level, the eighth LED (LE8) is turned on.

Next, an example of the operation of this input / output circuit is shown in FIG.
The timing chart will be described.

Between times t11 and t12, times t13 and t14
During the period between time t15 and t16 and during the period between time t17 and t18, both the first and second select signals S1 and S2 are L level, the third select signal T3 is L level, and the fourth select signal T4 is H level, 4 dual-purpose ports (IO1) to (IO4) are both high level, so the first dual-purpose port (IO1)
Is the first switch (SW1), the second combined port (IO2) is the third switch (SW3), and the third combined port (IO3) is the fifth switch (S
The state of the seventh switch (SW7) is read at W5) and the fourth combined port (IO4).

Between times t12 and t13, times t14 and t15
During time t16 to t17 and during time t18 to t19, both the third and fourth select signals T1 and T2 are at H level, the first select signal S1 is at H level, and the second select signal is
Since S2 is at L level, the first to fourth LEDs (LE
1) Output operation for (LE4) is performed. Of these, from time t12 to time t13, the first dual-purpose port (IO
1) is L level, second to fourth combined ports (IO2) to (IO4)
Since it is at H level, only the first LED (LE1) lights up. From time t14 to t15, the second combined port (I
O2) is L level, and the 1st, 3rd and 4th combined ports (IO
1) (IO3) (IO4) is H level, so 2nd LE
Only D (LE2) lights up. From time t16 to t17, the third combined port (IO3) is at L level, and the first, second and fourth ports are
Since the dual-purpose ports (IO1) (IO2) (IO4) are at H level, only the third LED (LE3) lights up. From time t18 to time t19, the fourth combined port (IO4) is at L level, first
~ Since the third combined ports (IO1) to (IO3) are at the H level, only the fourth LED (LE4) lights up.

From time t19 to t20, time t21 to t22
During the period from time t23 to t24 and from time t25 to t26, the first and second select signals S1 and S2 are both at L level, the third select signal T3 is at H level, and the fourth select signal T4 is at Since the L level and the four dual-purpose ports (IO1) to (IO4) are all high, the first dual-purpose port (IO1)
Is the second switch (SW2), the second combined port (IO2) is the fourth switch (SW4), and the third combined port (IO3) is the sixth switch (S
W6) and the fourth combined port (IO4) read the status of the eighth switch (SW8).

Between times t20 and t21, times t22 and t23
During time t24 to t25 and during time t26 to t27, the third and fourth select signals T1 and T2 are both at H level, the first select signal S1 is at L level, and the second select signal is
Since S2 is at H level, the 5th-8th LED (LE
5) Output operation for (LE8) is performed. Of these, from time t20 to time t21, the first dual-purpose port (IO
1) is L level, second to fourth combined ports (IO2) to (IO4)
Since it is at H level, only the fifth LED (LE5) lights up. From time t22 to t23, the second port (I
O2) is L level, and the 1st, 3rd and 4th combined ports (IO
1) (IO3) (IO4) is at H level, so 6th LE
Only D (LE2) lights up. From time t24 to t25, the third combined port (IO3) is at L level, and the first, second and fourth ports are
Since the dual-purpose ports (IO1) (IO2) (IO4) are at H level, only the 7th LED (LE7) is lit. From time t26 to time t27, the fourth combined-use port (IO4) is at L level, first
~ Since the third combined ports (IO1) to (IO3) are at H level, only the eighth LED (LE8) lights up.

In the case of the input / output circuit of FIG. 1, a dual-purpose port
Since (IO1) to (IO4) can be switched to input operation and output operation in time division, if the number of input devices and output devices is the same,
The number of dual-purpose ports (IO1) to (IO4) is half of the total number of input ports (I1) to (I4) and output ports (O1) to (O4) of the conventional example in FIG. Since only two ports of the third and fourth select signal terminals (T1) and (T2) need to be added to switch the input operation and the output operation, the total number of ports can be reduced. Further, this difference becomes larger as the number of connected input devices and output devices increases.

[0030]

According to the input / output circuit of the microcomputer of the present invention, as described above, one input / output port can perform both input operation and output operation, and the number of required ports can be reduced. .. Therefore, a large number of input / output devices can be connected to a smaller number of ports, and a better man-machine interface can be realized.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram of an input / output circuit of a microcomputer showing an embodiment of the present invention.

2 is a timing chart showing an example of the operation of the circuit of FIG.

FIG. 3 is an electric circuit diagram of an input / output circuit of a microcomputer showing a conventional example.

4 is a timing chart showing an example of the operation of the circuit of FIG.

[Explanation of symbols]

(1) Microcomputer (SW1) (SW2) (SW3) (SW4) (SW5) (SW6) (SW7) (SW8) Switch (Input device) (LE1) (LE2) (LE3) (LE4) (LE5) (LE6 ) (LE7) (LE8) LE
D (output device) (IO1) (IO2) (IO3) (IO4) I / O port

Claims (1)

[Claims] 1. An input / output circuit of a microcomputer connected to a plurality of input devices and output devices, wherein an input / output port that also serves as an input port and an output port is provided, and the input / output port is time-shared. An input / output circuit of a microcomputer, which is designed to be switched between input operation and output operation.