Patent GB-959826-A (GB)
Title: Improvements in or relating to arrangements for the selective extraction of information stored on a magnetic drum
Inventor: CLARK THOMAS HAROLD
IPC: H04M15/32
Filed: 1960-02-05
Abstract: 959,826. Automatic exchange systems. BRITISH TELECOMMUNICATIONS RESEARCH Ltd. Jan. 26, 1961 [Feb. 2, 1960], No. 4227/60. Heading H4K. An operator extracts a subscriber's accumulated meter fee total, from its register among a number distributed round a track of a magnetic drum, by dialling the address of the register one digit of which address causes a marker to be moved across the corresponding number of groups of ten sections on a control track and another digit of which moves the mark across the corresponding number of sections in the selected group. During extraction of the fee total the mark is moved step-bystep across elements of the control track corresponding to elements of the wanted register. The arrangement described serves 1000 subscribers by means of a single regenerative track, the meter fee registers being accommodated on 10 tracks. Subscribers are connected to their registers from 5 control tracks, each containing 200 auxiliary sections. The auxiliary sections are, in consequence, only half the length of the meter fee registers and make it necessary to group the subscriber's registers according to odd or even numbered addresses. The use of the auxiliary sections in the control tracks is not described, but is mentioned to explain the complication of the numbering scheme employed. The regenerative track is divided into 21 sections corresponding to the pulses TD1 tc TD21 and each of the sections is further subdivided into 10 sections corresponding to the pulses TC1 to TC10. The section TD21 is used for timing the impulses of the dialled digits received from the operator and for storing the first digit. The sections TD21 of the other tracks are not used to allow track-switching transients to die out before information handling begins. Each auxiliary section on a control track is one TC pulse in length and the registers on the meter fee tracks are each 2TC pulses long. Each TC pulse embraces 12 binary elements TA1 to TA12. A meter fee register is located in response to a three-digit number, a marker being set up in the section TD10 or TD21 depending on whether the first digit is even or odd. The first digit is stored to govern the selection of a register track, depending on whether the third digit is odd or even. The second digit steps the marker one TD section for each impulse and the third digit then steps the marker one TC section for each impulse. This leaves the marker one element ahead of the required meter fee register. The meter fee register tracks are switched cyclically by the pulses TW1 to TW10 and when the appropriate TW pulse occurs, as indicated by the stored first digit, the marker in the regenerative track initiates the read-out of the first element of the wanted register. At the same time as the element is read out the marker is advanced one element to control read-out of the second element when the register track is next scanned. This proceeds for the first 12 elements, TA1 to TA12 of the register. A further 8 elements are then read out without the aid of the marker. The state of each element of the register is transmitted as a synchronizing pulse followed by no pulse, if the element is unmarked, or by a pulse if the element is marked. Notation.-A write signal for the regenerative track is given by output SBC, and an erase signal by SAC. A bit read out of the regenerative track gives a signal SLC, and no bit read out gives a signal SLC. The corresponding signals read out of a register track are SLM and SLM. Pulses TBO, TBE are representative of all odd or even TC pulses; pulses TWO, TWE representing the odd or even track pulses TW. Detailed description.-Timing functions. Before dialling the operator makes a key which establishes the line closed condition made manifest to the magnetic drum by a signal PIA, Fig. 1. In the last element TA12 of section TC3 of pulse TD21 the line closed condition causes toggle MAE to be set one element ahead of the time at which MAE is normally set by the absence of a mark in the first element TA1 of section TC4. With MAE set in TA1 of TC4 a mark is made in this element to indicate that the line is closed. Should MAE be reset during element TA12 of TC3 this mark is automatically erased. Toggle MAE is reset at the end of the TC4 section and is only set in element TA1 of TC4 during a revolution if the line is closed. A timing function must be exercised on the line condition to distinguish between inter-pulse pauses and inter-digital pauses and also to detect an extended line open condition to effect clearing down. If the line closed condition persists until the next TW1 pulse (once in ten revolutions) then a mark is made in element TA2 of TC4 to join the mark in TA1. Should MAE reset at this point both marks are erased. If, however, MAE stays set from element TA1 to TA12 until the second TW1 pulse then toggle MBE is set to time out the interval and causes a third mark to be made in TA3 or TC4. This third mark resets MBE ahead of its normal reset circuit and prevents the signalling of more than one inter-digital pause. If the line opens MAE does not set in TA12 of TC3 and neither is it set in TA1 of TC4 since this element contains a mark during the first revolution in which the line is found open. While serving its purpose to hold MAE reset the mark in TA12 of TC3 is automatically erased and with MAE reset the timing marks in TA2 and TA3 of TC4 are erased also. At the next revolution of the drum, therefore, toggle MAE is set by the absence of a mark in element TA1 of TC4 in TD21, this absence also effecting the setting of toggle MEE. As no mark exists in TA3 of TC4, MEE is reset two elements later. The timing function is pursued as before except that no mark is made in TA1 of TC4. That is, if MAE persists in its condition of being repeatedly set from element TA2 to TA12 until the next TW1 pulse, a mark is made in element TA2 and, if this persists until the second TW1 pulse, MBE operates to mark the element TA3. The mark in TA3 of TC4 prevents the resetting of MEE which sets with MAE and the presence of MEE set for a whole revolution causes erasure of the regenerative track in the TW1 period as well as restoring the drum circuitry to be described. By this means the timing function distinguishes between an impulse and the longer break in the calling loop that signals a clear down. For the purpose of the next paragraph it is important to note that when MEE stays set it prevents the resetting of MBE by the mark in TA3 so that in consequence a mark is made in TA4 of TC4 to indicate that the line has cleared down and to this extent erasure by MEE is not complete. Registration of impulses.-At each line open condition, as explained above, the toggle MAE is held reset for a whole revolution and this allows an impulse repeating toggle MCE to be set in element TA3 of TC4 in TD21. With MCE set the circuit shown in Fig. 2 causes an output SAC to erase the mark in TA4 left by the previous clearing down and produces an output SBC to mark the element TA5 with the permission of reset toggles MAF, MCF, these toggles also causing the immediate resetting of MCE due to the absence of a mark in TA5. No further action is taken until the line closes (in default of which MEE clears down), when MAE is again set in TA12 of TC3 to time out an inter-digital pause. Assuming further impulses arrive, the next impulse is repeated by MCE which causes an output SBC to replace the mark in TA4, the next impulse erases this mark and puts a mark in the next vacant element which is TA6, the next impulse restores the mark in TA4, and so on. As will be appreciated, this process registers the digit in elements TA4 to TA9 on a biquinary scale, the first impulse putting no mark in TA4 and putting a mark in TA5 and a mark in TA4 then indicating the impulse even and no mark indicating the impulse odd. As permitted by reset toggles MAF, MCF, of Fig. 2, the toggle MFE, Fig. 1, is set or reset to repeat the odd or even mark in TA4. In consequence the SBE output circuit of Fig. 2 causes a marker to be put alternately in element TA12 in section TC1 of TD10 or in element TA12 in TC1 of TD21 according to whether the impulse is even or odd. By this means the marker indicates one of two starting points depending on the odd or even character of the first digit. In response to the first interdital pause toggle MBF is set in the timing circuit and causes toggle MAF to be set in the sequence counter of Fig. 2. In this counter MBF will be set at the end of the second digit while MCF will be set at the end of the third digit and will supervise extraction of data. These sequence toggles stay set over a period and do not require a setting circuit for each revolution. When the impulse train of the next digit is received it is repeated, as was the first digit, by toggle MCE. Since MAF is now set the elements TA4 to TA9 of TC4 in TD21 remain intact. However, whenever the marker left in TA12 of TC1 of TD10, or TA12 of TC1 of TD21, is read it operates toggle MDE, Fig. 1, provided MCE is set by the first impulse. MDE remains set until over the SBC output circuit of Fig. 2 it replaces the marker in TA12 of TC2 of TD10 or TD21 at which time it resets MCE and is reset itself. The second impulse moves the marker forward by another TC section and so on. The interdigital pause detected at the end of the second digit by MBE, sets MBF in the sequence counter of Fig. 2 and the presence of MBF set modifies the reset circuits of toggles MCE and MDE and the SBC output circuit of Fig. 1 so that the marker is erased from its residual position in an element TA12 of a section TC1 and re-written into successive elements TA12 of sections TC2, TC3 &c., in response to the receipt of successive impulses in the third digit. In its final position the marker will lie one element ahead of the meter fee register from which data is to be extracted. The end of the third digit causes MBE to be set and MCF in the seq