Bit-Slice Design: Controllers and ALUs

by Donnamaie E. White

Copyright © 1996, 2001, 2002 Donnamaie E. White



Table of Contents

1. Introduction

2. Simple Controllers

3. Adding Programming Support to the Controller

4. Refining the CCU

5. Evolution of the ALU

6. The ALU and Basic Arithmetic

7. Tying the System Together





Last Edit Ocober 10, 1996; July 9, 2001

Advantages of VLSI

If bipolar has been chosen over MOS because of speed, LSI is preferable to SSI/MSI and VLSI is preferable to LSI for the same reasons.

First, costs are reduced with the larger devices. VLSI and LSI require fewer parts and therfore fewer boards and therefore less rack space. (One ASIC VLSI chip can replace a large, 14-layer fully populated SSI/MSI board.) There is less external etch and fewer pin connections as more of the interconnections are moved inside the chip.

Second, using LSI improves reliability. Approximately 80% of the failures of working systems are caused by broken etch or bent pins and other broken external connections. This is mechanical failure. Using SSI/MSI a typical controller might use 300 16-pin DIPs, for a total of 4800 pin connections. The same controller done with LSI might use 30 40-pin DIPs, for a total of 1200 external pin connections, the other interconnections having been moved to the inside of the device.

The AMD 2900 Family was used in this text. At the time it was published, the 2900 Family was considered industry-standard for bipolar bit-slice devices. It is a microprogrammable family of LSI-level complexity. Table 1-2 summarizes its advantages.

Table 1-2 Microprogramming with LSI - Advantages over SSI/MSI designs

  • More structured organization
  • Field changes - may be as simple as replacing a PROM
  • Adaptations - may be as simple as replacing a PROM
  • Expansions - preplanned, may be as simple as replacing or adding a PROM
  • Better documentation
  • Hardware and firmware can be designed in parallel
  • LSI uses fewer parts
  • LSI has better reliability
  • Diagnostic PROM can aid debug, maintenance

The Am2900 Family

Note: Check out the AMD website - the 2900 family has a third-party emulation available. The Am2900 Family itself is no longer in production. I get e-mail.

As of 1981, the Am2900 family included

  • CPU-ALU Am2910, Am2903, Am29203
  • Microprogram sequencers and controllers Am2909/2911, Am2910
  • Bipolar memory, error detection and correction controllers and support devices, Am2960 series
  • Interrupt controller Am2914, Am2913 and AM2902
  • Bus I/O Am2950, etc.
  • DMA support Am2940, Am2942
  • Timing support via microprogrammable microcycles, Am2925
  • Main memory program control, Am2930, Am2932
  • 16-bit Am29116

Consider a simplex block diagram of a basic computer, shown in Figure 1-1. The essential blocks of this diagram are:

  1. the CPU (central processing unit), containing the ALU and scratchpad registers, the PC (program counter) and MAR (memory address register(s))
  2. the main memory (RAM) where active programs and data are stored
  3. peripherals, including back-up memory, input, output
  4. the CCU (central control unit), which supervises everything else and contains the control logic instruction decode and the PROMs

Figure 1-1 Simplex system block diagram





The CPU is where data is processed; the CCU is where instructions are processed.

From this simple overview (a Von Neuman architecture) , progress to Figure 1-2 and the generalized computer architecture blocked out to show the various members of the 2900 Family and their applications. [Dated material]

Figure 1-2 Generalized computer architecture


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Copyright © September 1996, 1999, 2001, 2002 Donnamaie E. White White Enterprises