Bellmac 32

The Bellmac 32 was a microprocessor developed by Bell Labs's processor division in 1980, implemented using CMOS technology and was the first microprocessor that could move 32 bits in one clock cycle. The microprocessor contained 150,000 transistors, and improved on the speed of CMOS design by using "domino circuits". It was designed with the C programming language in mind. After its creation, an improved version was produced called the Bellmac 32A, then cancelled along with its successor, the "Hobbit" C Reduced Instruction Set Processor.

History

The teams that developed the Bellmac 32 were in three different locations: AT&T Bell Labs in Indian Hill (Naperville, Illinois), AT&T Bell Labs in Holmdel, New Jersey and AT&T Bell Labs Murray Hill, New Jersey.

As they did not have an automation tool, every chip designer had to use colored pencils to the completion of the initial design. Later, Steve Law developed a program that enabled the digitization of the initial designs.

The development of the Bellmac 32 produced a novel circuit design called "domino logic". The use of this technique was a breakthrough for the production of the microprocessor. Tests were carried out during manufacture that indicated a clock frequency even higher than 4 MHz target speed was possible. Implementing the control logic, however, proved unexpectedly complicated. Because of these complications, when the entire chip was finished and tested, speeds achieved only 2 MHz. The team saw it as a step forward, but not as successful, as it could not meet the initial AT&T plan.

After this failure, the working group had many meetings to develop agreed Bellmac 32A, as a second generation of Bellmac microprocessor. CMOS technology was chosen again and target clock frequency was 6.2 MHz Adjustment to maximize the size of transistors and resistors minimizing interconnections was fundamental in meeting the specifications. A 20-foot-by-20-foot plot of chip layout was produced and placed on the floor of a large room.[1] Once all work was done, testing revealed the chips produced not only overcame the frequency of 6.2 MHz, but many made it to the 7.8 MHz or even 9 MHz.[2]

After the breakup of AT&T, Bell Labs passed to Western Electric, and with this, the Bellmac 32 was renamed the WE 32000. Updated versions of the chip included the WE 32100 and WE 32200.

Architecture

The Bellmac 32 has a pipelined architecture with an instruction fetch unit that serves to control access to main memory, and an execution unit which serves to monitor the process and manipulate data.

The instruction queue is filled with the instructions fetched from the memory. The address arithmetic unit serves for address calculations.

Bellmac 32 hardware was able to store all instructions, data and register contents associated with a process during a context switch.

Registers

Bellmac 32 has a program counter and 15 general-purpose 32-bit registers. Three of these are used to support the operating system and can be used when the microprocessor is in kernel mode. It has three other registers that are used by some instructions as stack pointers.

Instructions

This microprocessor has 169 instructions, which are geared to run programs written in the C programming language. Therefore, the format of the string is adapted to the specifications of C and includes instructions to handle and transfer control procedures between them.

The instructions may have up to three operands. A major drawback is that there are no floating-point or decimal arithmetic instructions.

Memory

The Bellmac 32 has different types of addressing, such as linear, immediate 8, 16 or 32 bits, registration, register indirect, short shift, absolute and indirect displacement of 8, 16 or 32 bits.

References

  1. ↑ http://greg.org/archive/2011/12/09/on_the_bellmac-32_and_perhaps_the_worlds_largest_plotter_pen_drawing.html
  2. ↑ http://www.ieeeghn.org/wiki/index.php/First-Hand:The_AT%26T_BELLMAC-32_Microprocessor_Development
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