push switch controller to its in position, and consequently, file protect is always ON.
Referring now to FIGURE 2 there is shown a means of commissioning and decommissioning the erase circuits. As previously stated one means of controlling the commissioning and decommissioning of the erase circuits is achieved through the computer itself. The computer 201 may be programmed so as to provide at selected times an FP ON signal. This signal is fed to trigger 202 which conditions AND gate 203. A sample pulse S samples the condition of this AND gate 203 and provided the computer has generated the FP ON signal, this AND gate 203 will provide a pulse at its output at sampling time which is fed to OR gate 294. The micro switch referred to in FIGURE 1 is generally indicated in this figure as 108. In the position shown here this micro switch is in the FP ON position. It is placed in this position by virtue of the fact that the push button 103 of FIGURE 1 is in the out position. The micro switch has a plurality of contacts schematically indicated as 296, 207, 203 and 209. They are all mechanically ganged by the mechanical linkage 210. In the position as shown there is an open circuit between the output of the OR gate 204 and the solenoid driver 211. Consequently, an FP ON signal from the computer has no effect on the solenoid 105. However, there is a closed circuit between the power supply 213 and one input to AND gate 214. Contact 207 closes the circuit between the negative side of the power supply 213 and this input to the AND gate 214. Consequently, AND gate 214 is blocked. The output of AND gate 214 to the erase circuits 215 provides an inhibit signal thereto to decommission the erase circuits. The erase circuits control the erase function of tape transport 221. The read/write functions thereof are controlled by the R/W control 237. An inadvertent erase signal will not energize the erase circuit. At the same time the negative side of the power supply 213 is connected through contact 207 to the input to inverter 216. The output of inverter 216 being up conditions AND gate 217. In order to check that the erase circuits are inhibited the computer generates a signal IS FP ON? This signal is also fed to AND gate 217 which is unblocked at sample time by sample pulse S to provide a signal to the computer indicating that the file protect is ON and that the erase circuits are inhibited.
If now we assume that the micro switch is in a condition where file protect is OFF then the switch 108 is moved in a vertical down position. Contact 208 provides a closed circuit between the output of OR gate 204 and the solenoid driver 211. An FP ON signal from the computer through OR gate 204 will by virtue of the solenoid driver 211 actuate the solenoid 105. The actuator of the solenoid will strike the push button 103 in FIGURE 1 causing it to move from its in position to its out position. The micro switch then sensing the out position of the push-push switch controller will move the linkage 210 to move the contacts of switch 108 in a vertical up direction. This as has been explained previously results in inhibiting of the erase circuits.
The computer may also generate an FP OFF signal which is fed to trigger 218. The output of trigger 218 is fed to AND gate 219 and when sampled provides the signal FP OFF. This FP OFF signal is fed to OR gate 220 and the output thereof is fed to the contacts of the switch 10S. With contact 2G9 of the micro switch, in the position as shown in this figure the solenoid driver energized the solenoid 105 to move the actuator against the push button, moving said push button to its in position. The contacts of switch 108 then move in a vertically down direction resulting in the conditioning of AND gate 214 by connecting the positive side of the power supply 213 through contact 206 to one input thereof. An erase signal from the computer through AND gate 214 will energize the erase circuits. At the same time the positive side of the power supply 213 is
connected to the inverter 216 which provides a down level ai the output thereof to AND gate 217 to block this AND gate.
Thus far there has been discussed the means of com
5 missioning or decommissioning the erase circuits through the computer by programming. As previously discussed this control may be achieved through the tape itself. The tape, as it is well known, may have a plurality of coded characters thereon. One such signal may be END OF
10 TAPE. When such a signal is read by the tape transport unit 221 it is decoded by the decoder 222 and fed to the trigger 223. This signal will set the trigger 223 to condition AND gate 224. The address of the tape cartridge being read is stored in the register 225. Additionally
j5 the address of all cartridges which contain master information on the tapes thereof are stored in a plurality of registers 226 and 227. If the particular cartridge being processed at the time, whose address is stored in register 225, is a cartridge having master data thereon, as indi
20 cated by one of the registers 226, 227, the compare circuit 228 will so indicate and condition AND gate 224. Consequently at sample time AND gate 224 is unblocked to provide the signal END OF TAPE FP ON. This signal is fed to OR gate 204. If at this time file protect is
25 OFF then the output of OR gate 204 by virtue of this signal will energize the solenoid 105 to cause the pushpush switch controller to obtain a file protect ON position. If at this time file protect is already ON, no change is initiated. %
30 Another signal which may be generated by the tape is the END OF FILE (EOF) signal. In conjunction with this EOF signal the tape may generate either an FP ON or FP OFF signal. The FP ON and FP OFF signals are special coded characters which may for in
35 stance be generated simultaneously with the EOF signal. Turning first to the EOF-FP ON signal the tape unit will first of all detect the presence of the EOF signal which is decoded by the decoder 229 to SET trigger 230 and thereby condition AND gate 231. If in conjunction
40 with this EOF signal there is also generated an FP ON signal then decoder 232 will SET trigger 233 and further condition AND gate 231. AND gate 231 is unblocked
■ at sample time to provide the EOF-FP ON signal to OR gate 204.
The condition of trigger 230 indicative of the EOF signal is also fed to AND gate 234. If in conjunction with EOF there is also generated the FP OFF signal, the decoder 235 will SET trigger 236 to condition AND gate 234 which at sample time will then provide the
50 EOF-FP OFF signal to OR gate 220.
In addition to the generation of the control signals for the erase circuit by the computer and the tape itself there is also provided a manual FP ON signal which is fed to OR gate 204 and the manual FP OFF signal which
55 is fed to OR gate 220. These signals may be generated by any conventional means such as a manually operated switch.
Thus far it has been shown where the commissioning and decommissioning of the erase circuits may be con
6Q trolled by the computer or by the tape itself, and it is to be understood that any technique capable of erasing data is comprehended within this specification. Additionally means have heen described in which a manual switch may be thrown to control the erase circuits. Some conditions
6g may exist wherein the tape in the tape transport being processed by the computer may contain master information at the beginning of the tape and non-master information at the end of the tape. Also in connection with such a circumstance it may be necessary to read the mas
70 ter data and then the non-master data and rewind the tape back to the master data and start the reading process over again. In such a circumstance, the tape may contain the master data, followed by an EOF-FP ON signal, followed by an FP OFF signal and then the non-master
75 data. It can be seen then that one may read the master