JPS599120B2 - PROM protection circuit due to incorrect programming of PROM writer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a PROM writer (wrlter) that writes to a PROM (programmable read-only memory). The purpose of the present invention is to provide an improved means for preventing PROMs from being damaged and alerting the operator to such problems.

It is a well-known fact that PROMs generally operate by applying voltage to the power supply pins e and Θ.
Places that are frequently operated, such as writers, use a socket type, and it is common to accidentally insert the PROM into the socket in the wrong direction.

In the past, measures were used such as cutting out a part of the PROM outer case and using that part as a guide, or attaching a caution plate with an arrow in the insertion direction for lock type IC sockets and the like.

However, this was insufficient and erroneous insertions were unavoidable. P
If a reverse voltage is applied to the power supply pin of the ROM, there is a risk of destruction, and preventive measures are required.
By the way, as shown in Figures 1 and 2, which will be described later, the power consumption increases due to the difference in impedance characteristics when a voltage is applied in the forward direction and when the voltage is applied in the reverse direction to the power supply pins 4 and e of the PROM. Differences in current can be found.

FIG. 1 is a diagram showing the current consumption characteristics of a general PROM.

11 of the curve 5 is the current consumption when the voltage is applied in the forward direction, and 12 of the curve 5 is the current consumption when the voltage is applied in the reverse direction. Voltage V1 to PROM
When this is applied, current IF flows in curve 11, and current IR4 flows in curve 12.

Then, when voltage V2 is applied, in curve 12 PRO
M destroys it. Therefore, from current 1R1>1F1, current 1
By providing a reference current 11 such that R1>11>IFI, it is possible to determine whether the PROM has been inserted incorrectly.
Figure 2 shows an example of PROM characteristics that vary depending on the manufacturer. 21 of curve 57 is the current consumption when voltage is applied in the forward direction, and 22 of curve 55 is the current consumption when voltage is applied in the reverse direction. FIG.

In any case, the characteristics are different in the forward direction and in the reverse direction.

FIG. 3 is a block diagram of one embodiment of the present invention.

1, 7, 14-20, 23-26 are resistances, 2, 3, 8,
9 is a transistor, 4 is an IC socket into which the PROM 6 is inserted, 5 is a comparator, 10 is a buzzer, 13 is a capacitor, 27 to 29 are diodes, 30 is an LED (light emitting diode), 31, Vc is a power supply, 32 is a voltage application signal,
33 is a reverse insertion signal, and Ref is a reference voltage.

In the initial state when the PROM 6 is not inserted into the socket 4, the voltage application signal 32 is 0V (volt), and the transistors 2 and 3 are in an off (0FF) state.

Therefore, from the power supply 31, a voltage of Therefore, the output of the comparator 5 is always at a low level. Next, when the PROM 6 exhibiting the characteristics shown in FIG. 1 is inserted into the socket 4 in the forward direction, the voltage 0ut supplied to the PROM becomes a voltage obtained by dividing the voltage IN by the high resistance 1 and the internal resistance 7 of the PROM 6. Since the level is higher than the reference voltage Ref at one terminal of the comparator 5, the output of the comparator 5 remains at a low level. Then, when the PROM 6 is inserted into the socket 4 in the opposite direction, the voltage 0ut supplied to the PROM 6 becomes a voltage obtained by dividing the power supply voltage IN.
Since the internal resistance 7 of the PROM 6 is smaller than that in the former case, that is, when inserted in the forward direction, the voltage 0ut is lower than the reference voltage Ret, the output of the comparator 5 is at a high level, and the alarm L
The ED3O emits light and the buzzer 10 etc. sounds to alert the operator.

Since the resistor 1 has a high resistance, it works to suppress the voltage and current applied to the PROM 6, and only a small voltage is applied to the PROM 6, so that destruction of the PROM can be prevented. PR
When writing or reading OM6, by setting the voltage application signal 32 to a high level, transistors 2 and 3 are turned on only when the reverse insertion signal 33 is at a low level, and the power supply voltage IN is applied to the PROM6. It turns out.

Thus, according to the present invention, when the PROM 6 is inserted into the socket 4 in the reverse direction, the reverse insertion signal 3 of the output of the comparator 5 is
3 becomes high level, an alarm is issued and the operator is notified, and even if the voltage application signal 32 is applied, the reverse insertion signal 3
3 is high level, transistor 8 is on, therefore transistors 3 and 2 are off; 7, so the power supply voltage VI
N is not directly applied to the PROM 6 as a voltage of 0ut, thereby avoiding destruction.

Furthermore, when the PROM 6 is inserted forward into the socket 4, no alarm is issued and the output of the comparator 5 is at a low level, so when the voltage application signal 32 is applied, the transistors 3 and 2 are turned on and the power supply voltage VIN becomes 0ut, which is applied to the PROM 6, and writing and reading can be performed. Therefore, the operator does not always have to pay too much attention to the insertion of PROM 6 into socket 4;
The workability of writing and reading PROM6 has been improved.
This completely prevents damage caused by reverse insertion of PROM6.
can be protected.

[Brief explanation of the drawing]

1 and 2 are characteristic curves of the voltage applied to the PROM and its current consumption, and FIG. 3 is a block diagram of an embodiment of the present invention. 1, 7, 14-20, 23-26...Resistance, 2
．． 3, 8, 9...Transistor, 4...
・IC socket, 5...: Comparator, 6.
・・・・・・PROMllO・・・・・・Buzzer, 13・
... Capacitor, 27-29 ... Diode, 30 ... LEDl3l, Vc ...
・Power supply, 32...Voltage application signal, 33...
...Reverse insertion signal, Vref...Reference voltage.

Claims (1)

[Claims] 1 PR for writing or reading PROM
In the power supply circuit of the OM writer, there is a circuit that detects whether the PROM is inserted into the IC socket normally, and the output of this detection circuit detects whether the PROM is inserted into the IC socket.
1. A PROM protection circuit against incorrect insertion of a PROM writer, characterized by comprising a circuit configured to control a voltage from a circuit that supplies power to a PROM writer. 2 When the PROM is inserted into the IC socket in the forward direction, the voltage supplied to the PROM is higher than the reference voltage and the comparator output that compares the two becomes a low level, and the PROM
If there is a voltage application signal to the power supply, the normal voltage from the power supply is PR.
When the PROM is inserted in the reverse direction into the IC socket, the voltage supplied to the PROM is lower than the reference voltage and the comparator output that compares the two becomes high level, activating the alarm circuit and sending the voltage to the PROM. 2. The PROM protection circuit according to claim 1, wherein a low voltage is applied to the PROM from a power supply via a high resistance even if a voltage application signal of 1 is applied.