Pascal MicroEngine
Encyclopedia
The Pascal MicroEngine was a series of microcomputer
products manufactured by Western Digital
from 1979 through the mid 1980s, designed specifically to efficiently run the UCSD p-System. Whereas other microcomputers ran a machine language p-code
interpreter
, the Pascal Microengine had its interpreter implemented in microcode
, so p-code was effectively its native machine language.
As usual on the p-System, the most common programming language
used was Pascal
.
The MicroEngine ran a special release III p-System, which was not used on any other platforms.
However, the enhancements of release III were incorporated into release IV which was made available for other platforms but not for the MicroEngine.
The MicroEngine chipset was based on the MCP-1600
chipset which formed the basis of the DEC
LSI-11 low-end minicomputer
and the WD16 processor used by AlphaMicro (each using different microcode).
One of the well regarded systems was the S-100 bus
based dual processor cards developed by Digicomp Research of Ithaca NY. These cards deserve an entry on their own, as they survived the demise of the WD single-board system and delivered reliable performance at up to 2.5Mhz. A typical configuration was a Digicomp dual processor board set, containing a Zilog Z80
and a bipolar memory mapper harnessed to a microengine chipset on the second board, linked by a direct cable. The sole configuration known to be still running in 2009 and documented on the web is described by Marcus Wigan, and contains 312kb of memory, RAM disc support, and uses – as all Digicomp Research systems did – a Z80 BIOS
to handle all the devices, allowing a range of floppy discs, I/O boards and hard disk controllers
to be used.
, Z80, and MOS Technology 6502 based systems). The MicroEngine could compile
Pascal source code in a fraction of the time (typically about 1/10) required by contemporaries. Fast compilation made the MicroEngine especially nice as a developer's machine, and the inclusion of a semaphore
primitive in the microcode was particularly useful for multi user enhancements, which were developed in Canberra, Australia (and possibly elsewhere). This performance advantage was eroded by the later availability of p-code to native machine code translators, and mainstream 16-bit microprocessors such as the Intel 8086
and Motorola 68000
.
When first announced the MicroEngine accumulated a very large number of pre-orders (for the time). The first boards shipped were poorly designed (power and ground traces the same size as signal traces, very few capacitors), required a large number of modifications, and even then did not work reliably. A couple of years would pass after introduction before a well-engineered MicroEngine was available. Between a damaged reputation and the introduction of the IBM PC
, in the end the MicroEngine was only modestly successful.
One example of a commercial product based on the MicroEngine was the AVAB Viking lighting control system, which used the Modular MicroEngine boards along with some custom hardware.
compiler using the Modular MicroEngine.
This compiler was later transferred to mainframe/minicomputers under the name of GenSoft Ada.
Ada was the only other full programming language available.
Due to limited memory (62K 16-bit words, the last 2K words being reserved for memory-mapped I/O
and PROM
for the hard disk bootstrap code) only very small Ada programs could be compiled. At one point in the compilation the compiler swapped the operating system out to disk, to gain just a little more room.
"A(da" replaced "A(ssmble"
on the main command menu. No native assembler was available or needed.
Microcomputer
A microcomputer is a computer with a microprocessor as its central processing unit. They are physically small compared to mainframe and minicomputers...
products manufactured by Western Digital
Western Digital
Western Digital Corporation is one of the largest computer hard disk drive manufacturers in the world. It has a long history in the electronics industry as an integrated circuit maker and a storage products company. Western Digital was founded on April 23, 1970 by Alvin B...
from 1979 through the mid 1980s, designed specifically to efficiently run the UCSD p-System. Whereas other microcomputers ran a machine language p-code
P-Code machine
In computer programming, a p-code machine, or portable code machine is a virtual machine designed to execute p-code...
interpreter
Interpreter (computing)
In computer science, an interpreter normally means a computer program that executes, i.e. performs, instructions written in a programming language...
, the Pascal Microengine had its interpreter implemented in microcode
Microcode
Microcode is a layer of hardware-level instructions and/or data structures involved in the implementation of higher level machine code instructions in many computers and other processors; it resides in special high-speed memory and translates machine instructions into sequences of detailed...
, so p-code was effectively its native machine language.
As usual on the p-System, the most common programming language
Programming language
A programming language is an artificial language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine and/or to express algorithms precisely....
used was Pascal
Pascal (programming language)
Pascal is an influential imperative and procedural programming language, designed in 1968/9 and published in 1970 by Niklaus Wirth as a small and efficient language intended to encourage good programming practices using structured programming and data structuring.A derivative known as Object Pascal...
.
The MicroEngine ran a special release III p-System, which was not used on any other platforms.
However, the enhancements of release III were incorporated into release IV which was made available for other platforms but not for the MicroEngine.
Products
The MicroEngine series of products was offered at various levels of integration:- WD-9000 five chip microprocessor chip set
- WD-900 single board computer
- WD-90 packaged system
- SB-1600 MicroEngine single board computer
- ME-1600 Modular MicroEngine packaged system
The MicroEngine chipset was based on the MCP-1600
MCP-1600
The MCP-1600 was a multi-chip microprocessor made by Western Digital in the late 1970s through the early 1980s. Used in the Pascal MicroEngine, the original AlphaMicro system, and the DEC LSI-11 microcomputer, a cost-reduced and compact implementation of the DEC PDP-11.There were three types of...
chipset which formed the basis of the DEC
Digital Equipment Corporation
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
LSI-11 low-end minicomputer
Minicomputer
A minicomputer is a class of multi-user computers that lies in the middle range of the computing spectrum, in between the largest multi-user systems and the smallest single-user systems...
and the WD16 processor used by AlphaMicro (each using different microcode).
One of the well regarded systems was the S-100 bus
S-100 bus
The S-100 bus or Altair bus, IEEE696-1983 , was an early computer bus designed in 1974 as a part of the Altair 8800, generally considered today to be the first personal computer...
based dual processor cards developed by Digicomp Research of Ithaca NY. These cards deserve an entry on their own, as they survived the demise of the WD single-board system and delivered reliable performance at up to 2.5Mhz. A typical configuration was a Digicomp dual processor board set, containing a Zilog Z80
Zilog Z80
The Zilog Z80 is an 8-bit microprocessor designed by Zilog and sold from July 1976 onwards. It was widely used both in desktop and embedded computer designs as well as for military purposes...
and a bipolar memory mapper harnessed to a microengine chipset on the second board, linked by a direct cable. The sole configuration known to be still running in 2009 and documented on the web is described by Marcus Wigan, and contains 312kb of memory, RAM disc support, and uses – as all Digicomp Research systems did – a Z80 BIOS
BIOS
In IBM PC compatible computers, the basic input/output system , also known as the System BIOS or ROM BIOS , is a de facto standard defining a firmware interface....
to handle all the devices, allowing a range of floppy discs, I/O boards and hard disk controllers
Disk controller
The disk controller is the circuit which enables the CPU to communicate with a hard disk, floppy disk or other kind of disk drive.Early disk controllers were identified by their storage methods and data encoding. They were typically implemented on a separate controller card...
to be used.
Reception
At the time of introduction, the only competitors were 8-bit processors (mainly Intel 8080Intel 8080
The Intel 8080 was the second 8-bit microprocessor designed and manufactured by Intel and was released in April 1974. It was an extended and enhanced variant of the earlier 8008 design, although without binary compatibility...
, Z80, and MOS Technology 6502 based systems). The MicroEngine could compile
Compiler
A compiler is a computer program that transforms source code written in a programming language into another computer language...
Pascal source code in a fraction of the time (typically about 1/10) required by contemporaries. Fast compilation made the MicroEngine especially nice as a developer's machine, and the inclusion of a semaphore
Semaphore (programming)
In computer science, a semaphore is a variable or abstract data type that provides a simple but useful abstraction for controlling access by multiple processes to a common resource in a parallel programming environment....
primitive in the microcode was particularly useful for multi user enhancements, which were developed in Canberra, Australia (and possibly elsewhere). This performance advantage was eroded by the later availability of p-code to native machine code translators, and mainstream 16-bit microprocessors such as the Intel 8086
Intel 8086
The 8086 is a 16-bit microprocessor chip designed by Intel between early 1976 and mid-1978, when it was released. The 8086 gave rise to the x86 architecture of Intel's future processors...
and Motorola 68000
Motorola 68000
The Motorola 68000 is a 16/32-bit CISC microprocessor core designed and marketed by Freescale Semiconductor...
.
When first announced the MicroEngine accumulated a very large number of pre-orders (for the time). The first boards shipped were poorly designed (power and ground traces the same size as signal traces, very few capacitors), required a large number of modifications, and even then did not work reliably. A couple of years would pass after introduction before a well-engineered MicroEngine was available. Between a damaged reputation and the introduction of the IBM PC
IBM PC
The IBM Personal Computer, commonly known as the IBM PC, is the original version and progenitor of the IBM PC compatible hardware platform. It is IBM model number 5150, and was introduced on August 12, 1981...
, in the end the MicroEngine was only modestly successful.
One example of a commercial product based on the MicroEngine was the AVAB Viking lighting control system, which used the Modular MicroEngine boards along with some custom hardware.
Other languages
A group led by David A. Fisher developed the third validated AdaAda (programming language)
Ada is a structured, statically typed, imperative, wide-spectrum, and object-oriented high-level computer programming language, extended from Pascal and other languages...
compiler using the Modular MicroEngine.
This compiler was later transferred to mainframe/minicomputers under the name of GenSoft Ada.
Ada was the only other full programming language available.
Due to limited memory (62K 16-bit words, the last 2K words being reserved for memory-mapped I/O
Memory-mapped I/O
Memory-mapped I/O and port I/O are two complementary methods of performing input/output between the CPU and peripheral devices in a computer...
and PROM
Programmable read-only memory
A programmable read-only memory or field programmable read-only memory or one-time programmable non-volatile memory is a form of digital memory where the setting of each bit is locked by a fuse or antifuse. Such PROMs are used to store programs permanently...
for the hard disk bootstrap code) only very small Ada programs could be compiled. At one point in the compilation the compiler swapped the operating system out to disk, to gain just a little more room.
"A(da" replaced "A(ssmble"
on the main command menu. No native assembler was available or needed.
External links
- Western Digital Pascal MicroEngine
- Pascal MICROENGINE documentation at bitsavers.org