Patent GB-1127270-A (GB)
Title: Data storage cell
Inventor: GARDNER PETER ALAN EDWARD
IPC: G11C15/04
Filed: 1967-09-05
Abstract: 1,127,270. Electric digital data storage. INTERNATIONAL BUSINESS MACHINES CORP. 5 Sept., 1967, No. 40623/67. Heading G4C. [Also in Division H3] A transistor binary storage cell, suitable for an associative store, provides the same first output signal whether it is in its " 1 " state and is interrogated for a "1" or is in its " 0 " state and is interrogated for a " 0 " and has a third state which also provides the first output signal whether it is interrogated for a " 0 " or " 1 ". The cell may have a fourth state which provides a different output signal when so interrogated. The storage cell in Fig. 4 comprises two bi-stable circuits arranged such that in state " 1 " T1 and T2 conduct, state " 0 " T1 and T3 conduct, state " 3 " T2 and T3 conduct and state " 4 " T1 and T4 conduct. Non - destructive interrogation for a " 0 " (i.e. a " 0 " match) is effected by switching the " 0 bit " a line 44 to - 0-2 V at switch 46 and the " 1 bit " line 45 to 0À1 V at switch 47. If the cell is in the " 0 " state transistor T1 is conducting but its emitter current is directed by the operation of switch 46 to emitter E12. T4 is non-conductive so that no current flows to the output line 43 from either transistor, indicating a " 0 " match. If however the circuit is in the " 1 " state the current from T4 is directed to the output line 43 indicating " no match ". Interrogating for a " 1 " match may be similarly effected and produces no current in line 43 if the match conditions exist. If the cell is in the third state neither transistor T1 nor T4 is conducting and no current flows to line 43, indicating "match" whether interrogation is for a " 0 " or a " 1 ". If however it is in the fourth state T1 and T4 both conduct and one or other current is directed to the output line 43 whether interrogation is for a " 0 " or " 1 ", indicating no match. Non-destructive read out may alternatively be effected by closing switch 49 on 0À1 V and switches 46 and 47 on 0 V. Current flowing from T1 or T4 into one or other of the bit lines 44 and 45 indicates the state of the circuit. Writing is effected by applying the interrogating voltage, such as from switches 46 and or/47, to the bit lines and lowering the threshold of the bi-stable circuits by closing switch 48 on the 2.0 V terminal and switch 49 on the 0À1 V terminal so that the transistors are into the conducting or non conducting states corresponding to the positions of switches 46 and 47. The previous state of the cell may first be destroyed by momentarily closing switch 48 on the floating terminal. If switch 49 is moved to the - 0À2 V terminal the data cell is isolated since the bit lines are then ineffective to direct the emitter currents to the output line 43. In Fig. 6 emitter followers are used in the cross couplings (as described with reference to Fig. 5, not shown) to avoid the necessity of hard saturation. In addition switch 48 is replaced by a switch 61 and the collectors of the emitter followers are taken to a tap on the collector resistors of the main transistors T1, T2, T3, T4. Interrogating and writing is carried out in a similar manner to Fig. 4 except that the lowering of the threshold to permit writing is effected by operating switch 61 to - V so as to increase the current through the emitter resistors and reduce the current through resistors R3b and R6b. Fig. 6 shows a circuit having only the first, second and third stable states, the states being represented by one of the main transistors T7, T8 or T9 conducting. These three transistors derive their input through respective emitter followers from the joint output of the other two main transistors so that any one of the main transistors will conduct only when the other two are non-conducting. Interrogating for a " 0 " is effected by placing such voltages on the bit lines 71 and 72 that if current is flowing in transistor T7 it is steered through emitter E71 to the " 0 " bit line to indicate match whereas if current is flowing in transistor T8 it is directed through emitter E82 to the word emitter line 73 to indicate no match. Interrogating for a " 1 " is similarly effected. If the circuit is in the third state (T9 conductive) no significant current reaches the output emitter lines 73 whichever interrogation is carried out and a match signal is indicated. A null interrogation is effected by placing such voltages on the bit lines that no significant current reaches the word emitter line even if T7 or T8 is conducting. Reading is effected by placing such a voltage on the word emitter line 73 that if current is flowing in transistors T7 or T8 it is diverted to the associated bit line to indicate the state of the cell. If T9 is conducting no current will appear on either line. Writing is effected by placing such a voltage on the word emitter line 73 that the switching threshold of transistors T7 and T8 is lowered and placing voltages on the bit lines 44, 45 such as to force the transistors T7 and T8 into the required conducting conditions. The cell is described in relation to an associative store (Fig. 1, not shown) in which the input register (11) is coupled to the columns of the store through a masking register (13). The cell enables one particular data position to be ignored without masking the whole of the column.