Patent GB-971312-A (GB)
Title: Flow table logic
IPC: G06F9/32
Filed: 1961-07-17
Abstract: 971,312. Sequential switching circuits. INTERNATIONAL BUSINESS MACHINES CORPORATION. July 17,1961 [July 29, 1960; May 16, 1961], No. 25759/61. Heading G4H. [Also in Division H1] Sequential switching circuits i.e. circuits adapted to manifest a series of conditions each of which can be reached by conditioning different ones of a number of inputs in a predetermined order are constructed by the following steps: - Expressing the operation of the circuit as a flow table in which the stable and intervening unstable states are represented in blocks arranged in columns representing inputs and rows representing conditions of the circuit; providing mutually insulated conductors for each row and column of the flow table; connecting a latching circuit for each block in which a stable state is represented between the row and column conductors specified by the corresponding block; connecting a latch actuating circuit between each latching circuit and the latching circuit associated with a succeeding stable state so that the circuit is switched from one condition to the appropriate succeeding condition when an input is conditioned. The method is based on the system for representing the successive operations of switching circuits, such as relay circuits, described in Chapter 12 of "Switching Circuits and Logical Design" by Caldwell. Such a flow table may be illustrated by Fig. 1 which represents the sequential operation of a push-button generator having three mechanically interlocked buttons designated R (reset), A and B, each adapted, when depressed, to stay down until a different button is depressed. Two buttons are always up and one is always down. The unstable states, i.e. the conditions between up and down, are represented by the numeral or letter unringed e.g. 2. The stable states are represented by numerals or letters ringed e.g. (2). Initially the R button is down and the device is in its stable state (R). In this condition the button A may be pressed to give the stable state (1) via the unstable state 1. If button B had been pressed instead an error condition would have been set up via E to (E) which is shown on the bottom line. When the device is in the (1) state, the button B may be pressed, 2, to put it in the (2) stable state. If the reset button R is pushed the device returns to the (R) reset state. If the A button, 1, is pressed again the device returns to the first stable state (1) and the sequence A-B-A-B repeats indefinitely. If the reset button is pressed when the device is in the (1) state this constitutes an error E giving rise, as before to the (E) state. In the flow table, therefore, each row represents a different stable state, shown ringed. The unringed letters or figures in a row represent possible inputs in that stable state, and the corresponding ringed letters or figures represent the resultant stable state. Fig. 2 shows an equivalent of the flow-table of Fig. 1 using neonphotoconductor components. Power is applied via switch 202 to line 203 and the switches 204,205,206 represent inputs R,A and B, applying power to column conductors 207,208 and 209. Row conductors 210-214 are provided. Certain cross points are connected by neons, e.g. 215, which glow when the corresponding input switch is closed and the corresponding row is grounded. Row wire 210 is permanently earthed at 232 but all the other row wires are floating at both ends. For each neon there is a photoconductor adapted to earth the corresponding row wire when their neons are glowing. Units in squares corresponding to unstable conditions are "PUT" units serving only to operate latch units in squares corresponding to stable states. These latter are called "TAKE" units and latch by being connected to earth their own row wires when the neon glows. When the R button is pressed, neon 215 glows and PUT unit 235 earths row wire 211 so that row wire 211 is earthed. Neon 216 then glows and unit 236 latches by earthing this row wire, power being still supplied through the switch R. This represents the (R) stable state. Similarly the latching TAKE unit representing each other stable condition is provided with at least one relaying PUT unit. In operation, closure of switch R causes resetting as described with TAKE unit 236 latched and cross wire 211 earthed. If switch A is now closed switch R releases and PUT unit 237 oper - ates to earth lead 212 illuminating neon 218 and photoconductor 238. Had switch B been closed the PUT unit 244 would have earthed cross wire 214 to operate the TAKE unit 245 representing an error, (E). In the (1) stable state, cross-wire 212 is earthed so that when the switch B is closed PUT unit 239 operates to earth the next crosswire 213 thereby operating the TAKE unit 240 corresponding to the (2) stable state. A second closure of switch A causes PUT unit 241 to operate, again to earth cross-wire 212 so that TAKE unit 238 operates again. Thus the A and B conditions alternate and switches closed in any other order cause the error TAKE units 243 or 245 to operate. In Fig. 3 the table is simplified by using triangles to represent the PUT units and circles for the TAKE units. Diamonds 356 indicate floating ends of wires and broken circles 357 the input signals. This is the form that the table may take when used for a circuit design. In Fig. 5 a similar table is shown for a circuit having six inputs A-F and arranged to recognise the sequence A-C-E each switch being released before the next is pressed, that is, after each switch operation, there is a "no switch" operation. The corresponding column is indicated by the word "NONE" with the circuit in the home position (H), the A switch may be pressed to operate the PUT unit 1 and transfer to first stable state (1). When the A switch is released the PUT unit 2 operates and actuates the TAKE unit (2). The process continues for the stable states (3), (4), (5) and (6). The PUT and TAKE units may be constructed as before of neon lamps and photoconductors. This circuit may be used as a lock to open a door. In a similar arrangement an alarm is provided actuated by an error circuit whenever the wrong switch is closed. For example switch B should never be used and a PUT unit is provided on each cross-wire so that if switch B is pressed at any stage an error TAKE unit is operated. A form adapted to be made by printed circuit techniques is shown in Figs. 12A- 12C, which corresponds to the sequential switching arrangement of Figs. 1-3. An array of electroluminors is formed on a glass plate 1250 as shown in Figs. 12A and 12C. The square elements 1215 &c. between the junctions of column conductors 1207, 1208, 1209 and row wires 1210-1214 glow when a voltage is impressed on them. The row conductors are transparent e.g. of tin oxide. The photoconductors 1235 &c. and conductors 1260, 1262 &c. are printed on a plate 1252 fastened to plate 1250 by rivets 1253-58 by which the crossconductors are connected to the earthed conductor 1260 when the corresponding photoconductor receives light from its electroluminor. When the R button is pressed element 1215 glows (R PUT), cross-conductor 1210 being earthed. This causes element 1235 to conduct and applies earth via rivet 1253 to cross-conductor 1211 to cause element 1216 to glow. Element 1236 accordingly conducts to maintain cross-conductor 1211 earthed. This is the TAKE unit representing the (R) stable state. The other steps are as described with reference to Figs. 1-3. In the form of Fig. 13 a similar sequence circuit is shown in which the PUT units (shown as circles in triangles) prime or precondition the associated TAKE units (shown as circles) by direct connection rather than by earthing the successive cross-wires. The circuits used use field effect transistors. A TAKE unit comprises a PN transistor 1450 and an NP transistor 1451, Fig. 14A each being made to conduct by earth signals applied at inputs 1452 and 1453. Normally positive output terminal 1454 then falls to earth potential. Point 1455 being earthed latches transistor 1451 in the conducting state bringing point 1456 to earth potential after the conditioning input 1452 is removed. The PUT unit consists of an NP transistor biased for conduction when cross-wire 1457 is earthed. The output 1463 then rises from a negative voltage to earth. This output is connected to the conditioning input 1452 of the next TAKE circuit, the final selection being on a column-wire connected to input 1453. The table of Fig. 13 is implemented using these circuits as shown in Fig. 15. When the switch R is closed column-wire 1507 is earthed and the TAKE circuit 1550 latches for the (R) stable state. This earths cross-wire 1511 causing PUT circuits 1551 and 1552 to condition TAKE circuits 1553 and 1554. If switch A is operated to earth column-wire 1508 the TAKE circuit 1553 latches for the (1) stable state. If switch B is operated to earth wire 1509 the error TAKE cir - cuit 1554 operates. Other sequential operations are similar. In the table of Fig. 16 the number of PUT circuits is reduced by having only one for each row i.e. one for each stable condition, which PUT circuit primes or preconditions a number of other TAKE circuits which operate when the associated column-wire is energized. Suitable units may consist of NPN transistors with resistive or gate inputs. In the form of Fig. 20 the PUT units are embodied in the TAKE units, that is each TAKE circuit conditions the TAKE circuits which may next be operated. Thus in the (R) stable state the (1) and (E) TAKE circuits are conditioned and will be operated by inputs A and B respectively and so on. Units for this form may consist of superconductive circuits Fig. 21. A column wire 2151 supplies current to input 2152 and it takes one of two available paths 2157,2158 to the terminal 2153 through TAKE connection 2154 back to source 2156. Where the paths cross at 2159 the magnetic field around line 2158 makes