• Home
  • Download PDF
  • Order CD-ROM
  • Order in Print
Core Address Selection
PACKETS

Fire Controlman Volume 03-Digital Data Systems
Page Navigation
  127    128    129    130    131  132  133    134    135    136    137  
of the core(s) to zero. If the core(s) had been in the one state, the sense line would pick up the change in flux direction from one to zero and indicate that a one had been stored in the core. At the completion of the read operation, the core or cores addressed are left in the zero state (three or four wire). The contents of the cores sensed by the read current would be temporarily stored in a register. This process of reading cores to the zero state is known as a destructive readout. Data read from cores must be temporarily saved in a register and then immediately written back into the cores  (restored). The destructive readout of data from cores necessitates the completion of the storage or memory cycle. WRITE  (RESTORE)  CYCLE.  —New data or the data read from core must be written (or written back) into the cores for permanent storage. This portion of the storage cycle is known as the write or restore operation. Each storage cycle consists of a read and then   a   write   or   restore   operation.   Other   terms commonly used are the read and write half-cycles. During the write or restore operation, write current is applied to the drive lines of the core or cores addressed. Write current is designed to change the state of a core from zero to one. Remember at this time all the selected cores are in the zero state from the read operation. For the four-wire cores that are to store zeros, inhibit current is applied through the inhibit line in opposition to the write current. The inhibit current prevents the changing of the core(s) from zero to one. Three-wire cores change to the ONE state only if both digit and word lines carry write current. Current in the digit line is dependent on the binary bit to be stored. The word line carries write current during the write operation. When the bit to be stored is a zero, no write current is applied to the digit line. Write current in the word line only will not change the state of the core to one. When a one is to be stored, write current is applied to the digit line, and when combined with the word line current, changes the state of the core to one. During the write or restore operation, all selected cores that are to store a one are written to the one state. All selected cores that are to store a zero will be in- hibited from writing a one by the inhibit current in the four-wire cores and left in the zero state. Lack of digit write current will leave three-wire cores in the zero state. READ/WRITE  CIRCUITS.  —Two  important circuits used during the read/write cycle include the inhibit current regulator and sense amplifiers. Inhibit Current Regulator. —The inhibit current regulator circuits are enabled only during a write cycle when there is zero in the corresponding bit of the interface register. The resulting inhibit current pulse prevents a one from being written into the associated bit position at the address selected. Sense Amplifiers.  —The sense amplifiers sense the state of the cores selected during a read operation. The sense amplifiers are disabled during a write cycle, and enable the sense amplifier strobe during a read cycle. Data read by the sense amplifiers is transferred into the interface register until it can be restored back into core memory. FILM MEMORY Film memory is the other primary storage medium of  digital  computers. It is used primarily on large mainframes. Depending  on  the  mainframe,  film memory is contained in  memory modules;  usually  four large memory modules to a mainframe computer set. Film Architecture Magnetic film storage is composed of hundreds of thousands of very small “I’’-shaped magnetic thin film spots. Figure 6-14 is an example of one film spot and Figure 6-14.—Bistab1e nature in thin film spots. 6-13






Western Governors University

Privacy Statement
Press Release
Contact

© Copyright Integrated Publishing, Inc.. All Rights Reserved. Design by Strategico.