JPH0542721B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a read/write circuit for a floppy disk used for reading information written on a floppy disk or writing desired information onto a floppy disk.

BACKGROUND ART As shown in FIG. 2, a conventional read/write circuit for a floppy disk has a read/write magnetic head (hereinafter referred to as magnetic head) 2 connected to terminals 11, 12 and a common terminal 13 in a write mode or a read/write mode. A mode switching circuit 4 is installed to set the mode, a write switch circuit 6 is installed to write information to the floppy disk in response to this mode switching, and a read switch circuit 8 is installed to read out information stored in the floppy disk. is set up.

The mode switching circuit 4 is provided with a read setting circuit 10a that sets the magnetic head 2 in a read mode, and a write setting circuit 10b that sets the magnetic head 2 in a write mode. Read setting circuit 1
0a is composed of _a transistor 20, resistors 22 and 24, and a switch _S1 . When the switch S1 is closed, the transistor 20 is conductive, and the power supply voltage Vcc applied to the power supply terminal 14 is applied to the transistor 20 and the resistor 22. The signal is applied from the common terminal 13 to the midpoint of the magnetic head 2 via. The write setting circuit 10b is composed of a transistor 26 and a switch _S2 . When the switch _S1 is open and the switch _S2 is closed, the transistor 26 becomes conductive and the power supply voltage Vcc is applied to the transistor 26 from the power supply terminal 14. It is applied from the common terminal 13 to the midpoint of the magnetic head 2 via the common terminal 13.

The write switch circuit 6 includes transistors 28,
30, constant current source 32, 34, 36, diode 3
8, 40, resistors 42, 44 and switches S ₃ , S ₄
The transistors 28 and 30 have a common emitter and constitute a current switch. That is, the magnetic head 2 is connected to the anode sides of the diodes 38 and 40 via the terminals 11 and 12.
A resistor 46 is connected to terminals 15 and 16 formed on the cathode side of the diodes 38 and 40. This resistor 46 is connected to the magnetic head 2 during writing.
This is a dump resistor for lowering the Q (Quality factor) of In this write switch circuit 6,
By alternately switching switches S ₃ and S ₄ ,
By switching the direction of the current flowing from the midpoint of the magnetic head 2, desired information can be written from the magnetic head 2 onto the floppy disk.

The readout switch circuit 8 includes diodes 48, 50, 52, 54 and bias resistors 56, 5.
_The floppy disk is read out when the switch _S5 is closed.

The information read out by the readout switch circuit 8 is applied to a preamplifier 68 and then to a signal processing system (not shown).

In such a read/write circuit, each circuit 4, 6, 8, 6 except for the magnetic head 2 and the resistor 46
Reference numeral 8 is composed of a one-chip semiconductor integrated circuit, and each switch S ₁ , S ₂ , S ₃ , S ₄ , S ₅ is composed of a switching transistor formed on the semiconductor integrated circuit.

According to such a read/write circuit, when the switch _S1 is opened to cut off the transistor 20, and the switch _S2 is closed to make the transistor 26 conductive, a write mode voltage is applied to the midpoint of the magnetic head 2. will be applied.
In this mode, by alternately switching the switches S ₃ and S ₄ of the write switch circuit 6, the excitation direction of the magnetic head 2 can be changed and necessary information can be written on the floppy disk.

Further, when the switch _S2 is opened and the transistor 26 is cut off, and the switch _S1 is closed and the transistor 20 is turned on, a read mode voltage is set in the magnetic head 2. In this state, when switches S ₃ and S ₄ are closed to cancel the operation of the write switch circuit 6, and switch S ₅ is closed and the read switch circuit 8 is activated,
The signals read by the magnetic head 2 from the floppy disk are transmitted to the resistors 56 and 58 of the read switch circuit 8.
is generated and applied to a preamplifier 68 where it is amplified.

Problems to be Solved by the Invention In such a read/write circuit, the read switch circuit 8 is composed of diodes 48, 50, 52, 54.
Each diode 48, 5
0, 52, and 54 are required to have a high withstand voltage of Vr > 24 (t) when the power supply voltage V _cc = 12 (V), for example, as a function of the generation of back electromotive force of the magnetic head 2. be done. That is, the voltage at the terminal 11 is the sum of the voltage V _cc and the forward drop voltage V _F of the diode 48 (V _cc
+V _F ) or less, only the resistor 56 is added to the load of the readout switch circuit 8, and if the voltage at the terminal 11 is more than (V _cc +V _F ) due to the back electromotive force, the resistor 5
The resistance value obtained by connecting 6 and 60 in parallel is added to the load. Such a relationship between back electromotive forces must be taken into consideration, making it difficult to implement a semiconductor integrated circuit.

In addition, the write setting circuit 10 of the mode switching circuit 4
As with the write switch circuit 6 and the read switch circuit 8, the power supply voltage V _cc is applied to b, so for example, when this read/write circuit is used in a portable device, V _cc = 5 (V). Run it with
Alternatively, in a device that requires a high voltage for the magnetic head 2, it is difficult to operate the entire circuit by changing the operating voltage over a wide range, such as operating at _Vcc = 12 (V).

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a read/write circuit which is suitable for semiconductor integrated circuit implementation and which allows the voltage applied to the magnetic head to be selected over a wide range.

Means for Solving the Problems The present invention provides a read switch that reads information from a floppy disk via a magnetic head in accordance with a read mode or a write mode set in a read/write magnetic head of the floppy disk by a mode switching circuit. In the read/write circuit for a floppy disk, the read/write circuit for a floppy disk is provided with a write switch circuit for driving the magnetic head and writing desired information on the floppy disk, wherein the read switch circuit is a collector input switch consisting of at least one pair of transistors. be.

Effect: By configuring the readout switch circuit with a collector input switch, it becomes easy to implement it into a semiconductor integrated circuit.

Furthermore, a read mode setting circuit in which a mode switching circuit is installed between the common terminal of the magnetic head and the first power source, and a second power source set to the same or higher voltage as the common terminal and the first power source are connected. By configuring it with a write mode setting circuit installed in between,
The voltage to be set on the magnetic head can be selected from a wide range.

Embodiments Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.

FIG. 1 shows an embodiment of a read/write circuit for a floppy disk according to the present invention, and the same parts as those of the read/write circuit shown in FIG. 2 are given the same reference numerals.

In FIG. 1, the read setting circuit 10a, write switch circuit 6, and read switch circuit 8 of the mode switching circuit 4, and the write setting circuit 10b of the mode switching circuit 4 are configured to be driven by power supply voltages of different systems. , the first power supply to the former circuit system is supplied to the power supply terminal 69, and V _DD is the voltage thereof. Further, the second power supply for the latter write setting circuit 10b is supplied to the power supply terminal 14,
V _cc is the voltage, and its value is set equal to or higher than the voltage V _DD .

The write setting circuit 10b of the mode switching circuit 4 is
Transistor 70, constant current source 72 and switch
Consists of S ₂ .

The readout switch circuit 8 is composed of a collector input switch consisting of at least one pair of transistors, and in this embodiment, transistors 74 and 76, constant current sources 78 and 80, and resistors 82 and 8
4 and switches S ₆ and S ₇ .

In addition, in FIG. 1, switches S ₁ , S ₂ , S ₃ ,
S ₄ , S ₆ , and S ₇ are composed of switching transistors on a semiconductor integrated circuit, and are configured to selectively open and close based on a predetermined switching input.

The operation of the above configuration will be explained.

(a) Read mode Close switch _S1 to turn transistor 20 on, and open switch _S2 to cut off transistor 70. Further, both switches S ₃ and S ₄ are closed to cancel the operation of the write switch circuit 6.

In this state, by opening the switches S ₆ and S ₇ , the read mode is entered.

At this time, a bias is applied to the base of the transistor 20 by the resistor 24, and the transistor 20 becomes conductive, so that the voltage V _DD applied to the power supply terminal 69 is applied to the base of the transistor 20 and the resistor 22.
The signal is applied from the common terminal 13 to the midpoint of the magnetic head 2 via.

That is, the current output from the common terminal 13,
The current is branched from the midpoint of the magnetic head 2 to the left and right terminals 11 and 12, and each current flows to the readout switch circuit 8.

Transistors 74, 7 of readout switch circuit 8
6, bias is applied to the base from constant current sources 78, 80, and each transistor 74, 76 is in a conductive state, so the current flowing into terminals 11, 12 passes through transistors 74, 76, and resistor 82. , 84 to cause a voltage drop. This voltage drop becomes a DC bias for preamplifier 68.

At this time, the magnetic head 2 is placed in a constant excitation state, making it possible to read out information stored on the floppy disk. As a result, the read signals generated at the terminals 11 and 12 of the magnetic head 2 are applied to the preamplifier 68 from the resistors 82 and 84 via the transistors 74 and 76 and amplified, and then sent to a signal system (not shown). communicated.

In such a read mode, the voltages V _cc , V _DD
is held at V _cc ≧ S _DD , and the cathodes of diodes 38 and 40 are pulled up to the voltage V _cc via resistors 42 and 44, so that the diodes 38 and 40
is placed in a cut-off state. Also, since switches S ₃ and S ₄ are closed, transistors 28 and
The base of 30 is placed at ground potential, and transistors 28 and 30 are cut off.

(b) Write mode Open switch S ₁ to cut off transistor 20, and close switch S ₂ to make transistor 70 conductive. Also, the switches S ₆ and S ₇ are closed, and the switches S ₃ and S ₄ are alternately switched.

At this time, the current output from the common terminal 13 via the transistor 70 passes through the midpoint of the magnetic head 2 and selectively flows toward either the terminals 11 or 12. That is, when switch _S3 is open and switch _S4 is closed, transistor 28
becomes conductive, so the current flowing through the magnetic head 2 flows from the terminal 11 through the diode 38 and the transistor 28 into the constant current source 34. Furthermore, when the switch _S3 is closed and the switch _S4 is open, the transistor 30 becomes conductive instead of the transistor 28, so that the current from the magnetic head 2 flows from the terminal 12 through the diode 40 and the transistor 30. The current flows into the constant current source 34.

That is, by alternately switching the switches _S3 and _S4 , the direction of the current flowing through the magnetic head 2 is changed, so that the direction of magnetization is reversed, and desired information can be read and written to and from the floppy disk.

At this time, switches S ₆ and S ₇ are closed, so
Transistors 74 and 76 are in a cut-off state, and current flow into transistors 74 and 76 is blocked.

In each mode, the voltage V _cc applied to the power supply terminal 14 can be set equal to or higher than the voltage V _DD ; for example, in a portable device, V _cc =Q(V),
V _DD =5 (V), and when using a high voltage magnetic head, set V _cc =12 (V) and V _DD =5 (V).

As explained above, the readout switch circuit 8
Since a collector input circuit consisting of NPN transistors 74 and 76 is used, the breakdown voltage between the collector and emitter of the NPN transistor is
Since the base-to-base breakdown voltage can be easily increased, it is easier to integrate the circuit into a semiconductor integrated circuit compared to the readout switch circuit 8 shown in FIG. When a conventional diode switch is used, the shape on the semiconductor integrated circuit is special and requires a diode that cannot be obtained using a general manufacturing process.

Further, when the transistors 74 and 76 are in a cut-off state, a back electromotive force is generated in the magnetic head 2, and a voltage approximately twice that of the common terminal 13 is applied to the transistor 7.
4 or the transistor 76, good cut-off characteristics can be obtained because the transistors 74 and 76 are NPN transistors.
Suitable for semiconductor integrated circuits.

Effects of the Invention As explained above, according to the present invention, semiconductor integrated circuits can be easily fabricated, and the voltage applied to the magnetic head can be selected from a wide range.
We can expect the product to become more versatile.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a read/write circuit for a floppy disk according to the present invention, and FIG. 2 is a circuit diagram showing a conventional read/write circuit for a floppy disk. 2... A read/write magnetic head, 4... A mode switching circuit, 6... A write switch circuit, and 8... A read switch circuit composed of a collector input switch.

Claims (1)

[Scope of Claims] 1. A read switch circuit for reading information from the floppy disk via the magnetic head in accordance with a read mode or a write mode set in the read/write magnetic head of the floppy disk by a mode switching circuit, and the magnetic head. A floppy disk read/write circuit comprising a write switch circuit for driving a floppy disk to write desired information to the floppy disk, wherein the read switch circuit is a collector input switch consisting of at least one pair of transistors. read/write circuit. 2. The mode switching circuit includes a read mode setting circuit installed between the non-conducting terminal of the magnetic head and the first power source, and a second read mode setting circuit installed between the non-conducting terminal of the magnetic head and the first power source, and a second read mode setting circuit installed at a voltage equal to or higher than that of the common terminal and the first power source. 2. A floppy disk read/write circuit according to claim 1, further comprising a write mode setting circuit installed between the floppy disk read/write circuit and a power source of the floppy disk.