PROBLEMS
1. For the example program given above, show a possible pattern of bits in the K(PCS) program memory, assuming a particular assignment of operation codes (see Chapter 2).
2. Write the BCD-to-Binary and Binary-to-BCD conversion subroutines required in the example program.
3. Write a program in the 16/M so that a program held in a M(array; 1024 words) is interpreted the same way that Crtm-1 would interpret it. Modify 16/M to improve the ability to interpret Crtm-1.
4. Try problem 3 for a PDP-8 or your favorite minicomputer.
5. Solve any of the application problems given in other sections. Compare the conventional RTM, K(PCS), and 16/M cost and performance (recall the analyses in Chapter 4). 6. Respecify the 16/M in ISP.
An RTM system can be interconnected to a general purpose computer in many ways, depending on the system objectives (e.g., cost and performance) and the computer being interfaced. No doubt the simplest interface is the T(serial), which only involves connecting two pairs of wires between the computer and RTM system, providing full duplex data transmission at 10,000 bits/second. Two other interfaces will be described which provide closer coupling and higher data transmission rates. A particular minicomputer is used to illustrate the transmission scheme. The structure of the simple minicomputer is shown in Figure Cl-1. All external devices are connected to the minicomputer by means of an In- Out Bus. This bus has two types of controllers:
Ks - Slow data transfer controllers - (Program controlled transfers) - Data transmission is accomplished by a program in Pc. Ks may request words by signalling using an interrupt request.
Kf - Fast data transfer controllers - (Direct memory access transfers) - Data transmission is accomplished by having Kf request words. Pc merely passes requests for data on to primary memory (Mp). In this mode the system looks like a random access memory to Kf.
In building an interface between RTM's and the minicomputer, the method used for transfer mainly depends on the needs of the RTM system for data. With minicomputers the programmed transfer method can be used for word transfer rates of perhaps 100,000 words/second, although this method is normally used at only 10,000 words/second because of the high processor utilization. The direct memory access methods are used for magnetic tapes and disks at speeds varying from 10,000 ~500,000 words/second.
In order to reduce processing time substantially the direct memory access method is usually used, and in some designs both interface methods are required. Both interface methods are presented in the following sections.
RTM MINICOMPUTER INTERFACE VIA PROGRAM CONTROLLED ACCESS
Figure Cl-2 gives most of the details for an interface between an RTM system and a minicomputer. The interface is full duplex in that data can be flowing quasi-simultaneously in both directions. The part of the interface nearest the minicomputer is constructed from two of the minicomputer's modules: a General Purpose Register Interface containing both an input and output register; and a
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