LC8008 Manual

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LC8008 Single Board Computer

User Manual

Introduction

The LC8008 Single Board Computer is a contemporary recreation of a mid to late 1970's prototype 8008 computer, utilizing the components and technologies available at the time. Certain components are actually of 70's vintage; this varies from unit to unit. The unit's primary purpose is to serve as an artistic showcase for the 8008 processor and the prototyping techniques of the 1970's. As the 8008 is the grandfather of the 8088 in the original IBM PC, and the heart of most of the first "micro" computers, it certainly ranks as one of the most important designs in computing and electronics history, ushering in the "microcomputer era".

Hardware Features:

8008 or 8008-1 Processor, Intel, running at 250 Khz (0.25 Mhz) with 8 Mhz crystal. The 8008-1 versions may be clocked to closer to the full rated speed of the 8008-1. To determine the clock speed of your unit, divide the number shown on the crystal (example, 8 Mhz), divide the speed shown by 16.

Highest quality available components are utilized (e.g., expensive gold-inlaid machined pin wire-wrap sockets, fiberglass tinned prototyping board)

Address lines fully TTL buffered - no "marginal" signals -usually found only on full-sized systems. Extensive bypassing.

2K of ultraviolet-erasable programmable read only memory (UVEPROM)

1K of random access memory (RAM), of which only 256 bytes are accessible in this design. The reason is described later.

Two 4-character 5x7 matrix LED displays, high-quality.

Oversized linear regulator, heat-sinked, and inverter for special 8008 -9 voltage.

Oversized UL-approved AC adapter

Power and error LED's

Processor status LED's (status LED's depending on model).

Power-on reset/reset switch (described below)

"True to period" design with no technology or chip unavailable in the '70's used (examples: no LCD displays, no green LED's, no 64K UVEPROM or flash,no monolithic capacitors, etc.).

Software Features

Power on self-tests for CPU, RAM, and ROM, display with diagnostic LED.

Message customizable at the "factory".

Receiving Inspection

A great deal of work and shipment testing went into the packaging. Use scissors or a cutter to remove the AC adapter and board from the box. Inspect for damage. It is fantastically unlikely, but possible, that a chip could come loose during shipment even though the best quality machined pin sockets were utilized.. See that the chips are not sticking out from sockets. If this should happen, email me immediately. You should save the packaging or at least remember how it was done for moving or reshipment. Plug the unit and turn it on. You will probably have to press the RESET switch (the only button on the board). The unit should display characters on the LED display.

Installation

Keep in mind that this is not exactly a consumer product. There is obviously voltage present on the board, and some of the components do get hot because they are designed to do so. No voltage is higher than +5 or -9, but nonetheless under bizarre conditions a shock or fire hazard could exist, especially if the unit is dropped or falls while unattended. Touching points on the board with metal (like that you might have on your finger, a ring) will probably cause serious damage to the board. A secure mounting is EXTREMELY important both for the safety of the unit and your own safety. Make sure that the "wall wart" cord is placed in such a manner that it cannot be tripped over.

It is important to make certain that the unit will not be in direct sunlight, for heat and other reasons, and out of the reach of bystanders.

Static Electricity

Integrated circuits are far less susceptible to static electricity when installed in a circuit. However, consider the following:

IC's can be "hurt" by surprisingly low static voltages that you could never feel when touching a doorknob, for example. These effects on
mean-time-before-failure (MTBF) are cumulative. You might knock a chip with a MTBF of decades down to a few years after several good "hits", even if it is not obviously damaged. The amount of "shock" required to do this is far less than a shock that you could feel.

The best policy is to avoid touching the unit's circuit board whether or not it is on; if it is to be in a public place, it should definitely not be accessible to touching. Remember, however, that the unit generates considerable heat, so ventilation is important.

UVEPROM Label

This label serves to identify the program contained in the UVEPROM and also to cover the chip's window. The window is made of a special glass that passes the UV rays that erase the chip. A special high-intensity (and dangerous) UV lamp is used to accomplish this; however, office lighting and especially sunlight will erase the chip at a much slower rate, but will nonetheless erase it. There are some 16,000 bits on the chip; one of them changing from a 0 to a 1 will cause the unit to fail.

Even under perfect conditions, the storage cells in UVEPROM's will eventually discharge, but this is thought to take decades under ordinary conditions with an opaque label covering the chip's window. For this reason, it is strongly recommended that you acquire the CD-ROM after executing a non-disclosure agreement (NDA). Sometime in the distant future, you or your heirs might need to have the UVEPROM reprogrammed!

Therefore, do not remove the UVEPROM label.

Self-test and Operation

Upon power-up, the unit will go into a self-test mode. Note: if you see no display, press the "reset" switch. The power-on reset circuit does not work under all conditions. You should see:

CPU PASS
RAM PASS
ROM PASS

LED TEST

Then, for one second or so, all LED's on the display should be lit. You should see no "holes".

The diagnostic LED will flash, once.

Should there be a failure, the diagnostic LED (in a slightly different location depending on unit) will flash with the code for the error. The reason
this is not displayed on the alphanumeric display is because a failure would definitely make this unlikely to function correctly. The codes are:

Two short flashes, long pause-CPU failure
Three short flashes, long pause-ROM failure
Four short flashes, long pause-RAM failure

See the Theory of Operation for more details.

Read This: Heat is NORMAL.

Certain components on the LC8080 get hot. Keep in mind that this board utilizes 1970's NMOS and PMOS technologies, which were not nearly as power-efficient as modern CMOS that you would find in your PC. Furthermore, all modern computers use "switching power supplies", which only pass the voltage and current required to operate the electronics. This board uses a brute force linear regulator, which dissipates excess power as heat. After testing, I have determined that under room conditions, the board will never get hot enough to burn persons or property. However, the uninformed might be startled or upset about the heat output. Here are the "hot points:"

1. LM323K Linear Regulator

This IC (it is an integrated circuit, not a transistor) is basically an integrated circuit built around a large pass transistor. Approximately 9 volts
go into the unit from the wall wart, and 5 volts is delivered to the board's circuitry. The rest is dissipated as heat. Higher voltages will be
dissipated as more heat, which might overheat the 323 and cause it to shut down. This is why it is extremely important that this AC adapter only be utilized to operate this unit.

2. 8008 CPU

With PMOS design and 10 micron features, this chip gets HOT. However, it is in ceramic, and designed to operate this way.

3. Displays

These displays do not get as warm as the LC8080's dumb displays, but they will get warm.

Theory Of Operation

(A more detailed version exists on the CD-ROM, available to the purchaser after execution of an NDA)

Power Supplies

The "wall wart" provides approximately 9.3 volts of power, which is fed to the LM323K linear pass regulator, where is is dropped to +5 volts. The "black box" beneath is a high-frequency DC-DC converter (yes, these did exist in the 70's-every HP calculator built from '72 to '80 had one!) creates -9 volts from the +9.3 volt input. The current requirement is very small for the -9. Bulk filtering via electrolytic caps is utilized on most outputs and the 323 input; bypass capacitors are used throughout the board, generally on a 1 to 1 basis with each IC, which is quite conservative.

Obviously, wire-wrap techniques are generally "noisier" than PCB designs, and this was deemed a requirement. The 8008 has extremely limited drive capabilities and even with NO peripheral chips connected, it is noisy. Oscilloscope displays show that the care taken in this design was worthwhile.The rear of the board uses +5 and ground busses.

+5 is used by every IC on the board.

-9 is used by the 8008.

Clock

The 8008 uses a +5 volt two phase clock created with the crystal and the 7493,'04, and '08 nearby.

CPU Main Data Bus

The 8008, having very few pins, requires a lot of external circuitry because the data and address lines must be derived from a common 8 bit bus. Proper data is produced on the bus at certain T states. The 8008 has 5 major instruction states;

ST1
low-order address data presented on bus.
ST2
high-order address data presented on bus.
ST3
the instruction is read.
ST4
An internal bus transfer..
ST5
Another internal bus transfer.

Minor states include:

STOP
After ST3, if there has been a HALT, this state is entered. It can only be exited by an interrupt. This is what happens when you press the "reset" switch.

WAIT
Between ST2 and ST3. If the READY line is brought low, the chip can wait for slow memory. The memory used in this board is fast enough to work at full, "no wait" speeds, and therefore the NOT WAIT line of the 8008 is tied to logic 1.

STI1
This state exists when there is an interrupt, and is a special case of ST1. In this case, an address is "jammed" onto the address bus and memory is made available from this location. In this manner, its is possible to do some fairly amazing things, like TTL based priority interrupt circuitry, or even add new instructions to the 8008. In this design, only an interrupt to location 0 is utilized, in order to (re) start the CPU.

The states are derived from the SY clock and the S0, S1, and S2 pins of the 8008. These are fed to the 74LS138 3 to 8 decoder. a 74LS74 and '08 produce special derivatives of these states for the address decoders and memory.

Address Data

The LS175's and 273 produce the addresses from the main bus, also buffering and cleaning up the extremely weak and noisy signals of the 8008. The '273 handles the lower addresses; the 175's handle the upper addresses to A12 (remember, only 16K addressable). The upper 175 produces memory timing signals further refined by the 00,04, and 08.

I/O Decoding

The 8008 has easy to use I/O, 31 outputs and 7 inputs (it is possible to use an input instruction for an output, as this board does). There are specific one-byte instructions for their use, each instruction defining a particular input or output, which today seems very odd. a '138 is used to produce these signals, which go to the 273 (or 373, depending how I built it - NOTE: they are not pin-compatible) near the displays. Interestingly, this board latches the output 273/373 with an INP 7 instruction. This saves TTL logic at the cost of a little code.

Interrupt/Reset

Interestingly, the 8008 has no actual "reset" pin. What one must do to start the CPU is to force an interrupt, and impose on the address bus a desired address. Interrupts cannot be presented to the 8008 asynchronously - they must be times with certain states (making the interrupt latency of an 8008 very unpredictable). This is accomplished with the pushbutton switch, a 7400, and a 74LS04.

RAM/ROM

The RAM is 1K by 4 bits wide; however, only 256 bytes are used in this design (the other address lines on the RAM are tied to ground. The memory is set up this way to save space and speed in code - one does not need to set up the DH register for a read (the RAM exists on all pages). However, you need to set it to the upper 8K for a write.

ROM

The ROM is UV-programmed in a special computer driven "EPROM blower". Naturally, it is only read, and permanently contains the program that operates the displays. It exists at address 0. The code starts with a RST 010 (restart at 8 - the 8008 and 8080 are octal-based machines), and the actually code begins there. This is needed because the reset is actually an interrupt and you need to get out of it.

Alphanumeric Displays

These are only nominally "period" for this board. They are actually probably smarter than the 8008 itself, but such displays did exist in the 1970's from IEE and Burroughs, although they were so expensive that they saw mostly military use. They are addressed like RAM chips.

Error Display

Bit 7 of the 273/373 is used for the error display. The LED connected to this bit is not usually lit. Note that the power on self tests cannot always display the cause of a problem, because the problem itself may render this impossible. However, the error LED is more likely to work than the full alphanumeric display, and this is why the error LED exists.

State Display

ST1,ST2,ST3,ST4, and ST5, are displayed on the column of 5 LED's respectively. The LED to the left is the STOPPED LED. Note that the ST3,4,and 5 LEDS are quite dim, because most 8008 instructions are one byte (except for jumps, loops, and so on - things requiring a target address).

Firmware

The firmware was written in assembler, and is not very elegant, mostly because I am fairly rusty (by 25 years or so) in coding for this chip. No assembler existed in MS-DOS for it so I had to cobble up one for myself. After assembly, code was downloaded to an EPROM emulator from a PC and tested. When the program is shown to work, a UVEPROM programmer is used to "burn" the chip.

MTBF and Endurance

How long, exactly, will this unit operate before failing? This is difficult to say. Although the wire wrap looks delicate, keep in mind that the technique actually produces tiny "gas tight" welds from pressure on each corner of the pin, and there are several wraps. Barring physical damage, overheating, voltage spikes, and other transients, here is what can go wrong:

The large tube type capacitors on the unit (not the small disks) contain a fluid that can dry out over time, especially with heat. This can cause the power supply to "ripple", causing the computer to misinterpret data and crash. In extreme cases, the chips can be damaged.

The transformer will eventually open, and will have to be replaced. This should be easy to acquire in the future, but note that it must have a capacity of at least 1.2A and a voltage of no less than 7.3 nor more than 9.5 volts.

The LM323K does get hot, and will someday fail. It contains shutdown mechanisms that hopefully will prevent it from putting to much voltage to the computer. It is a common and inexpensive part and has been in production for 20 years or more. Hopefully, it will be available in the future.

The chips packaged in ceramic (which, until recently , were the only type the military would buy or permit to be used) are far less vulnerable to this phenomenon. Note that the high-value, most irreplaceable chips in the LC8080 are ceramic.

UVEPROMS are not "permanent" storage, although they are used this way often. They contain transistor cells that trap a charge. These charges, even without UV light, will eventually leak away. The time is measured, theoretically, in decades. I have not seen this happen although I have EPROMS that were programmed over twenty years ago. Nonetheless, it will eventually happen. This is why I provide the code on a high-quality CD-ROM, which, under good conditions, is thought to be stable for 50-100 years.

I mention these things as an aid in repairing the board for future generations of geeks!

Limited Warranty

The customer agrees that this is a special purpose, non-consumer device with special care requirements beyond typical consumer electronics. The device is sold as a curiosity and artwork, and not as a computing device.

The unit is covered by a limited warranty for one year for failure of a component or faulty labor. Exceptions to the limited warranty include, but are
not limited to, the following:

1. Physical damage, e.g., dropping the unit or bending wire wrap pins on the rear.

2. Disassembly of the board from the mounting.

3. Removal or modification of components

4. Static damage

5. Damage caused by improper line voltage or lightning

6. Improper mounting and/or ventilation

Repair or replacement of components will be accomplished with like components; however, given the rarity of the components used, exact physical replacement availability is not guaranteed (although a "safety stock" has been put aside for such eventualities). However, all reasonable efforts will be made to keep the unit as close to that originally sold as possible.

You acquire this unit with the understanding that my total liability is limited up to the purchase price of the product.

Bottom line is, I'll do what I can to reasonably accommodate any problems if you take reasonable care of the unit. However, I'm not exactly wealthy, so don't bother to get the ghost of Melvin Belli after me!

Software (Firmware) License:

You are licensed to use the software contained in the unit ("firmware"). You are not authorized to copy, modify, disassemble, reverse engineer, decompile, or transmit the firmware to other parties, or store it in any form on any information retrieval system, or to permit others to do so.

A copy of the source code, object code, simplified schematic sufficient for repair of the unit, memory map, and other details can be obtained on CD-ROM from the designer for $5.00 after execution by the customer of a signed non-disclosure agreement. This is recommended, as I hope that the 10 or so LC8008's that I build will be working far into the future, whereas, I'm not a young man, and I might not be working by then!

A Brief History of Intel and the 8008

This is a summary of documents available on the Internet and recollections from my memory.

Intel, short for Intelligent Electronics, was started in 1969 to produce semiconductor memory. At first, it was named "Moore-Noyce", but Bob Noyce and Gordon Moore saw that more noise was a Bad Thing in the electronics arena. Intel enjoyed modest success in its narrow field of business.

Although there are those who would argue this point, most would agree that Intel developed the first microprocessor, the 4004. It was a four-bit chip, released in 1972, designed for use in a calculator. Although Intel developed it exclusively for a customer, because of some bad luck on the customer's part and good luck for Intel, Intel retained the rights to the design and all of the technology they had developed in order to produce it.

Four bits was not enough to easily deal with character based data, and the 4004 was missing critical functions (like interrupts) that would keep it from being used in a "real" computer cost effectively. So Intel designed the 8008. Still slow, the 8008 had interrupts, a stack, and 8 bits. The 8008 achieved some success, although the speed was a disappointment to Intel - the original 8008 failed to meet its design goals. The 8008 was also a true horror to design a computer with - Intel put it in an 18-pin package, not nearly enough pins to deal with all of the signals a computer needed for input and output. These signals had to be recreated by external circuitry - circuitry that cost board space, power, testing time, money, and so on. This circuitry involved some real digital voodoo, and this, combined with Intel's horrible documentation at the time, made the chip very difficult to use in a computer, much less to write software for. Later, the 8008-1, a selected 8008, met the original design speed goals of the chip - still very, very slow. A very few computers that could be thought of as "personal" were designed, built, and sold with the 8008 CPU, but these were not very popular due to their high expense and very limited capabilities. The Scelbi 8H, the "Mark 8" computer, the RGS, and the Martin Research "Mike" computers are the only 8008 machines of which I am familiar. Incidentally, the LC-8008 is very similar in design to the Martin Research "Mike-4" computer, and much is owed to its designer, Don Martin, whom I once worked for, in keeping the chip count down. The contrast between the "Mark-8" computer and the Mike in terms of clenliness of design is tremendous. To be fair, microcomuputers were a "black art" then.

Software was scarce and the talent to write it was even more so. The only attempt I have ever seen in an 8008 high level interpreter was Scelbi's SCELBAL, a BASIC-like language, which, while a tremendous accomplishment, was very slow. We all take PC's for granted now, and I developed this board and firmware in an apartment room, but at the time, it took 5-15,000 USD of equipment to develop software/firmware for the 8008.

So, the 8080 was designed, and released in 1974 at a list price of $360.00, just for the chip! In 1974, you could get a drivable used car for that kind of money. An engineering fraternity at my university "scammed" Intel by creating a paper corporation, requesting samples, and getting a box of cosmetically defective 8080's for free! I myself remember paying $25.00 for an NEC 8080 in about 1976 after I destroyed my original chip with a slip of a voltmeter lead. I was making about $3.00 an hour at the time. Intel did a much better job of supporting the 8080 than they did with the 8008, and the 8080, while not nearly as easy to design with as today's micros, was much simpler to work with than the 8008. As far as I know, the 8008 was second sourced only by one Canadian company, which, incredibly, made the chips better than did Intel itself (they were unoffficially clockable at higher speeds).

Bill Gates and Paul Allen used the 8008 in their first commercial product, a traffic counter.

When the 8080 was introduced, virtually all new design work with the 8008 ended.

The 8080 was soon replaced by the 8080a, which was electrically improved, although there were no new instructions and it wasn't any faster. Virtually all 8080 designs commercially produced in quantity were of the 8080a variety. The famous MITS Altair 8800 used this chip, and when combined with Bill Gates' BASIC, which he sold through MITS, the machine was actually practical for business and home use (for very wealthy homeowners).

The rest, as they say, is history.

Of course, the 8088/86,286,386,486,Pentium /II/III generations came later. But the 8008, with it's 3,600 transistors, started the "micro" revolution. You can read more on Intel's web site - look up "History". There is a nice microphotograph of the 8008 on their site, which I use, ghosted, for wallpaper on my PC. After considerable reasearch, I have reason to beleive that less than 1,000 8008 computers presently exist in the entire world (only 200 SCELBI 8B/H's were built) - even most of the serious and deep-pocketed computer collectors and museums don't have one - but now you do. Most of those machines don't work and/or have no software to run. You have a working 8008 and firmware for it to run. Take care of it. It won't take care of you, but take care of it anyway!