JPH0235385B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a data protection circuit in a read/write control circuit for a magnetic device that prevents a read command from changing to a write command due to a failure of the write control circuit and destroying data on a magnetic medium. It is.

Conventionally, the configuration shown in FIG. 1 is often used for a read/write control circuit that decodes a write command from a host device to a magnetic device, performs write/read switching control, and outputs a write instruction signal. That is,
The instruction code from the host device is transferred to the instruction decoding circuit 1.
After inputting and decoding the output and checking the output for errors in the instruction decode check circuit 2, the write signal is passed through a write signal enable circuit 3 and a disable circuit 4 to a latch circuit 5 consisting of a flip-flop (FF). Set and reset in response to write and read commands. The latch output of the latch circuit 5 is outputted as a write instruction signal to the magnetic device, and further a drive signal is sent out via the AND circuit 6 and the driver circuit 7. In this case, if the circuit 3 that enables the write signal fails for some reason and the output set signal is fixed, the write instruction signal will not be sent to the magnetic device even though it is instructing the magnetic device to read. data on the magnetic medium will be destroyed.

An object of the present invention is to provide a read/write control circuit for a magnetic device that prevents data on a magnetic medium from being destroyed by generating a write signal during reading due to a failure of the read/write control circuit.

In order to achieve the above object, the read/write control circuit for a magnetic device of the present invention includes an instruction decoding circuit that decodes an instruction code from a host device, and a write signal sent to the magnetic device when the output of the instruction decoding circuit is a write instruction. a flip-flop circuit that is set when the output of the command decode circuit is a read command and reset when the output is not a read command; an AND circuit that gates a write signal of the flip-flop circuit with a reset signal of the flip-flop circuit;
The present invention is characterized by comprising a circuit that outputs a failure signal to a host device on condition that both the outputs of the set signal and the write signal of the flip-flop circuit are rising.

The present invention will be described in detail below with reference to examples.

FIG. 2 is an explanatory diagram showing the configuration of an embodiment of the present invention.

The difference between this figure and FIG. 1 is that after the output of the instruction decode circuit 1 is checked by the instruction decode check circuit 2, a flip-flop (FF) 1 is connected in parallel to the enable/disable circuits 3 and 4 described above.
1, and in the case of a read command, the Q output outputs a high level “1” and the output outputs a low level “0”.
In the case of a write instruction, the output is made at the above-mentioned inverted level. Then, the Q output of the latch circuit 5 and the output of the FF 11 are input into an AND circuit 6, and a drive signal is sent to the magnetic device via the driver circuit 7. As a result, when the enabling circuit 3 fails, the setting of FF5 is fixed and remains set even when a read command is issued. In that case, the output of FF11 will be low level "0", so the output of AND circuit 6 will be prohibited.
No write drive signal is sent to the magnetic device. Therefore, destruction of data on the magnetic medium can be prevented.

In addition, the Q output of the latch circuit 5 and the Q output of the FF 11 are put into a newly provided AND circuit 12, and when both outputs occur simultaneously, a high level "1" is output.
Flip-flop FF13 is set and a failure signal is sent to the host device.

As explained above, according to the present invention, in order to prevent data on the magnetic medium from being destroyed due to a read command changing to a write command due to a failure of the read/write control circuit for the magnetic device, this state is prevented from occurring. Also, when a read command is output, the write drive signal is prohibited from being sent, and when a write instruction signal is generated during a read, a failure signal is sent to the host device. In this way, it is possible to prevent data on the magnetic medium from being destroyed.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a conventional example, and FIG. 2 is an explanatory diagram showing the configuration of an embodiment of the present invention. In the figure, 1 is an instruction decode circuit, 2 is an instruction decode check circuit,
3 is an enabling circuit, 4 is a disabling circuit, 5 is a latch circuit, 6 and 12 are AND circuits, 7 is a driver circuit, and 11 and 13 are flip-flop circuits.

Claims (1)

[Scope of Claims] 1. An instruction decoding circuit 1 that decodes an instruction code from a host device, and an output of the instruction decoding circuit that sends a write signal to the magnetic device when it is a write instruction, and if it is not a write instruction, the write signal is sent. a flip-flop circuit 11 which is set when the output of the instruction decoding circuit is a read command and reset when the output is not a read command; Gate with the reset signal of the flip-flop circuit 11
A magnetic device characterized by comprising an AND circuit 6 and circuits 12 and 13 that output a failure signal to a host device on the condition that both outputs of the set signal and the write signal of the flip-flop circuit 11 are high. read/write control circuit for