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alternatively consider them to be unsigned integers or bit vectors). The 8, 12, or 16 bits of a register, R, are usually denoted R<7:0>, R<1 1:0>, or R<15:0>, respectively, thus giving both the range and the numbering to be assigned to each bit position in the register. For example, the bits of. R<7:0> are numbered from left to right, R<7>,R<6>,...R<0>. When interpreted as an integer, the j-th bit would have the value of 2^j. In some cases, when needed, bits are numbered in the opposite order <0:15>.

Associated with each data type is a full complement of appropriate data operations. This allows the user to selectively treat a 16-bit data word as a vector, for instance, if he limits himself to using only operations that apply to that data type. The data operations are more appropriately listed later, in. association with the DM modules that implement them.

Signal Types and Designations in Diagrams

The RTM Bus. The Bus carries the data among the registers for the various register transfer operations. All the DM, M, and T modules connect to it for inter-register transfers. Two signals, Bus DONE and Bus POWER CLEAR, connect to all control modules. The Bus is shown in Figure 9. There are two categories of signals on the Bus -- data signals, and control signals. The data signals correspond to the 16 bits of a data word and are denoted DATA<15:0>. There is a 17th link which carries OVERFLOW\OVF (actually carry) information. There are four Bus control signals -- POWER CLEAR which initializes the RTM system when it is turned on, and three internal Bus transfer sequencing signals that are essentially invisible to the RT level user. K modules are implicitly connected (i.e., prewired) to the pertinent control part of the RTM Bus to use the sequencing signals. A special control module, Kbus, is connected to the Bus for the purpose of controlling and defining it.

In the schematic diagrams used in this book, the Bus is denoted either as a single line or parallel lines (I or II) and a module connection to the Bus is denoted "___" or "==" (see Figure 6).

Control Part Signals. There are- two types of control signals in RTM systems. One type is carried by the links that pass control from K module to K module, called control flow links. In the schematics, these links are shown as solid lines (____). The other type of signal is passed from K modules to the data part of an RTM system to evoke data operations, along evoke-operation links. These links are drawn in the RTM diagram of Figure 6 as ( ____ ____ ____ ); in subsequent chapters, these links will normally not be drawn, or if they are drawn, they will be shown as solid lines (possibly labelled). All the various styles of lines used in this chapter are used to avoid confusion while introducing new material. In' subsequent chapters, however, we use mostly solid lines for compactness and simplicity.

Boolean and Other Data Signals. Single bit Boolean data signals may be passed between the control and the data parts of an RTM system and also solely within either part. A link carrying this type of signal is shown in Figures 2 and 6 as a dashed line, (-------); in subsequent chapters it will be shown as (b <Name>
or ( <Name> >).Conventional combinatorial switching circuits can be used to form functions of Booleans.

Other Signals. These signals are those whose form is not directly usable by the


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