ROM Chips l l A ROM chip is one or more chips on a pcb located in a rack or backplane/motherboard. Figure 6-35 is an example of a 64K ROM block diagram and IC with pin l connections. Notice the items used to obtain the ROM Magnetic (fig. 6-36) Transistors-Bipolar  or  MOS  (fig.  6-37;  MOS ROM) Fusible links Regardless of the type of material used for ROM, address. The heart of the chip is the 65,536-bit memory the cell array is masked to a particular 0/1 arrangement array. This array is masked with a ROM data pattern. The desired word in the array is selected by the X and to form the permanent data needed for ROM operations. Y decoders. The 13 address lines are the inputs to these two decoders. As the address is decoded, the output word is presented to the output buffers. The chip select line is used to enable or disable the tristate mode of the output buffers. The eight output lines come from the output buffers. Pure ROM chips are manufactured with the desired software instructions or data installed. READ-ONLY MEMORY (ROM) MATERIALS The types of materials that make up a ROM also vary. ROMs can consist of the following types of materials: READ-ONLY MEMORY (ROM) OPERATIONS As  stated,  ROM  operations  are  characteristic  of main memory operations except you cannot write to ROM. This means ROM operations use no write pulses or equivalent and no data input buffers are needed. The basic operation of ROM, like a main memory address, is to use the permanent data stored in the ROM address. Since we are studying the computer and its internal operations, the operation in this case is the  execution  of  an  instruction  contained  at  a  ROM address. But you can see where if you needed to use the same  data  at  a  particular  location  repeatedly  (for l Hardwired (fig. 6-36) example, a look-up table), this concept could be used. Figure 6-35.—ROM chip: A. Block diagram; B. Pin arrangement. 6-28


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