One of the complications of working with Digital Group systems was the different ROMS that could be used to startup the system (Audio, Phimon, Diskmon, OASIS, MCSO). Later in the chronology, if you had a Disk system, you could run a program called DDBOOT after booting into Diskmon to allow you to boot into the other operating systems. One solution was the ROM Switcher detailed in Bridge Vol.1 No.3 from August 1978. Another option was the UnROM outlined by Dr. Suding in this short article. This application was used to change ROMs on the TVC card (video interface). I'm certain that there are several articles about using the same method for the 1702a on the CPU card. I'll update this post and article when I locate the details.

"The UnROM"

by Dr: Robert Sudlng

Theory:

The 1702A EROM on the epu card may be remotely disabled by putting a low level signal on memory line Y. This circuit will Initially place a high level signal when turned on. An output of anything to Port 377 will disable the EROM: An output to Port 376 will return to the EROM.

Similarly, the 6S71L maybe disabled and replaced by some alternative character generator pattern. In this case, the 6571L Is removed from the D.G. TVC, Inserted on the supplemental "UnROM" board and the "UnROM's" cable is plugged Into the former 6571L on the TVC. Initial power on will enable the normal 657lL. An output of anything to Port 375 will disable the 6571L, and enable one of the 2708 EROM'S. Since the 6571L has an effective 16K bits of ROM, two 2708's are required, the first one handling the 1st 64 characters, and the second holding the last 64 characters. An output to Port 37. will enable the 6571L.

(Click on schematic at right for full size version)

The card may be inserted into any 22 pin I/O connector.

Parts:

1 - 7400
1 - 7410
1 - 7430
1 - 7442
2 - 74125
2 - 2708 (programmed with upper and lower)
1 - 6571L (removed from TVC)
1 - 22K 1/4 W resistor
3 - :01 disc capacitor
3 - 1 mfd tantalum capacitor
1 - 22 mfd tantalum capacitor
5 - 14 pin IC sockets
1 - 16 pin IC socket
3 - 24 pin IC sockets
1 - Dual 22 pin socket card
1 - Approx: 18" ribbon cable with 24 pin plug


Operation:

After correctly wiring card, remove 6571L from TVC and Insert on card. Plug Into any available I/O 22 pin connector. Insert the 24 pin plug Into the former 6571L socket on the TVC: Turn on the system. To UnROM, load a RAM version of the desired EROM; Out 377; Move the RAM version to address 000000ff; Proceed with the program. Similarly output to Port 375 to enable the APL character set ( or other desired set). Output to Port 374 to return to the standard ASCII.

Following is a summary of a two hour questlon and answer period with Dr. Robert Suding. Included here are a number of unpublished stories, fixes and comments of interest to Digital Group system owners. For ease of use, the material has been broken down by category. Those interested in hearing a tape of the entire session should contact Rich Kurtz.

Hardware Fixes and Notes

If you are having trouble with your TV-Cassette board., be sure to check the +5 volt supply at the board...it should not exceed 5.05 volts. Higher than this will cause a multitude of welrd problems. The 5 volt supply has a pot to adjust the output voltage. Bringing the voltage down will also make the system less noise prone. Try to shoot for 4.75 volts at the farthest memory board for the best results.

Having read errors on your Phi-Deck system? ... This can be cured by running a wire from the motherboard ground plane to the nearest chassis screw. This will also eliminate many other noise problems. What happens is that the Phi-Deck head lines pick up as much as .8 volts of video noise. Installing the ground eliminates 9O% of this noise. This also will eliminate hum problems in the Votrax system.

There are now modifications to the floppy dlsk board to allow its use with dynamic RAM. This is also what has been holdlng up the disk software. It is being made compatible so that the disk will not cause wait states which will loose the data in the dynamic chips. This means that OASIS, OPUS, Disk-Mon, MINI-MON, etc. will be released in the near future with all of these modifications.

There are design flaws in the Z-80 chips themselves... when you press the reset button on the computer, the z-80 goes to invalid TTL states once in a while in the memory request line. This will mainly cause problems with dynamic memory, causing your software to self-destruct ...to reset with dynamics, it is neceseary to modify the CPU card to reset using the non-maskable interrupt, thus avoiding the problem with the hardware reset. To modify the board...move the 220 Ohm resistor to the right of the CPU chip (R6) to the holes below the Z-80 chip. You are now ready for dynamics. This will have no affect on the operation of static memory except to allow plug in compatibility with all boards.

The video graphic board being demonstrated has 128 x 128 resolution with 16 grey levels. It can be built on a proto card for about $20.00 in parts. The schematic is available from Dr. Suding at no charge or see Walt Chalberg at a meeting for a copy.

RF problems either entering or leaving the system?... 1) Is the cover on? 2) Bypass the power cord. 3) Shield the fan and ground the body of the fan to the chassis. 4) Check your cables for radiation. The keyboard cable can be bypassed with a .01 mfd capacitor between the Strobe and +5 and another between +5 and Ground at the paddle card connector. If you look It the D.G. cabinet, you will flnd a whole bunch of tiny holes around the front and back panels. Those are meant to mount bronze "fingers" to make contact with the top and bottom to make it really RF tight. Of course, the vent holes will also have to be screened. The major radiation, however, will be from the power cord. Be sure to install those .01 mfd capacitors.

Misc. Information

On a new CPU Card:

"... The one that looks the most promising is the 6809. The 6809 by Motorola..,is not compatible with the 6800. It internally works like a 16 bit processor. It has hardware multiply capability somewhat similar to the TI but will support a lot of memory..."

On a 16 Bit CPU Card:

"....My plan tentatively is to design a new motherboard that has 2 CPU slots. You can either plug in your 16 blt processor into that slot or your 8 bit processor into that slot, all the other connections would be made for you and that's all there is to It. So you would exchange your motherboard (Which represents an investment of 40 or 50 dollars) now you can run 16 bit or 8 bit world. That's the plan of attack."

On New Products:

"Those of you who have the HAM board...you have a diagnostic in there that allows the system to self-diagnose (problems). ...Not only will you have the hardware perfect, you will have all the support software and you will have self diagnostic software (on all future products). What we are seeing is a vastly superior support in software for products being delivered. This means fewer products being introduced."

In bringing up a brand new out of the NEVER OPENED BOX phi-deck drive I was looking through some old tapes and ran across a copy of PHIDOC.TX which contains the updated documentation for PHIMON. This version "communicates" in hexidecimal instead of octal as well as supporting updated commands.

Enjoy


<PHIMON-H>: Hexidecimal PHIMON Ver 3.0
An addendum to the PHIMON OPERATING SYSTEM Manual

P.J. Ferrell K7PF


I. INTRODUCTION

<PHIMON> is a superior tape-based Operating System, exceeding the capability of man y disk-based systems. The modifications described herein are only extensions, and retain the design philosophy so ably expressed by David Bryant, the originator of <PHIMON>.

Some internal addresses have been changed due to 8080 code being replaced by more concise Z-80 instructions. Where possible, however, compatibility with previous versions was maintained. With the exception of HEX communication instead of Split-Octal, the user will notice little in the way of difference between <PHIMON> and <PHIMON-H>.


II. COMMAND EXTENSIONS

1) The DAte command replaces the HElp command.

2) The LOad command allows other than .GO extension, and permits optional starting address override using "@":

Format: >LO#n NAME.EX @addr

where addr is a two-byte hexidecimal address used instead of FPAGE (normally obtained from the header block).

3) SAve command allows other than .GO extension.

Format: >SA#n NAME.EX xx-yy*sa

Note that if .EX is not specified, a .GO default is assumed for LOad and RUn as well as SAve. If repeated saves of the same file are desired, all after the first can be accomplished by:

Format: >SA#n

NAME.EX and xx-yy*sa then default to their former values.

4) The ZEro command allows cassette length specification.

Format: >ZE #n Cxx
or: >ZE! #n Cxx

Legal values for xx are 30, 45, 60 and 90. If the Cxx is omitted, a C30 is assumed. Note the space following the #n is not optional, since nCxx is a perfectly legal HEX quantity, and GETNUM will return and xx for drive number!

5) The DName command allows changing (or adding) a cassette directory tape name. Automatic date insertion is optional.

Format: >DN#n

Tape drive selection is made with the #n (defaults to 0). the directory is read and the current name (if any) is displayed. A new name may then be entered. At any time, the "ESC" key will causes a return to PHIMON without modifying the present directory name. If name input is terminated with the RETU?N key, the current PHIMON date is included automatically. This autodating feature may be avoided by terminating input with the LINE FEED key rather than wit the RETURN key.

6) The DRefresh command will re-display the currently memory-resident directory listing. It will load the DIRECTORY overlay if necessary.

7) DTO/DTH has been replaced by STEPER. If the top 8K of memory is available, a DT command will execute STEPPER if resident or load and execute it if not.

III. ADDITIONAL FEATURES

1) All numeric communication with PHIMON-H is in HEX, including page numbers for the SAve command.

2) Upon booting up, <PHIMON-H> display as the current version's build date and asks for today's date. Date entry is free field, with any delimiter echoing as a /. Each program saved under this system includes the date in the header block. The LOad and RUn commands will display the save date after reading the file header block.

3) When initializing a directory with the ZEro command, a tape-name is requested. This may include up to 48 characters, and the current date is automatically appended. The DIrectory command will display the tape name along with the content listing. To correctly list a directory, <PHIMON-H> requires a name (try an old tape and see), but adding a name does not otherwise affect the old directory (try that too). Use the "DN" command described above to add a name. The name resides in the last half of the last block of the directory, reducing the maximum number of directory entries from 101 to 88.

4) The new PIP is one page smaller (8080 to Z-80 again) but has some new features. Rather than blindly continue after an error, it requests: "(SPACE) TO CONTINUE". Any other character will cause PIP to finish up with what it already has transferred.

5) An NMI (non-maskable interrupt) will force a re-boot of PHIMON without otherwise affecting memory content. This feature is best appreciated with trying to save an hour's worth of input with a clobbered copy of PHIMON.

6) Existing system tapes may be converted to <PHIMON-H> without disturbing their content. Place an old tape in drive #1 and a new <PHIMON-H> tape in drive #0, and type:

>BU #1

The boot-code and overlays of the old tape will be replaced by that of <PHIMON-H>.

Just added a very intersting article from "Brown Box Journal", March 1982 describing digital group history from Microworks point of view. The article can be found here or you can find it in the History section of the articles page.

Early 2005: I was fortunate enough to find a system that was still running albeit in a strange configuration. When I received the system, it was in pretty "odd" shape. While it seemed to work well, the guts were very unusual for a dg system. The normally fragile memory boards had been replaced by a CPU piggyback card with 64k on two chips! There was also a special purpose PROM board that held three switchable PROMs. The case was in good shape with only a few scratches. The front panel was immaculate as were the other anodized aluminum parts. The toughest part was the keyboard which had some keys that were intermittent and the whole thing was yellowed from smoking.

Since the system was working, I was hesitant to just tear the thing apart so I started with the keyboard. With a great deal of advice from Bryan Blackburn, I carefully disassembled the keyboard and spent days cleaning each individual key cap with #0000 steel wool and various cleaning agents. I carefully cleaned the circuit board, reassembled and tested it out.... perfect!

Fastforward to early 2007: A couple of moves and several other obligations kept me from this most enjoyable hobbie for several yeas. In that time I was fortunate enough to find two other systems, both seriously neglected but with some good boards and other stuff. One find included two brand new Phi-Deck drives still in the original boxes!!!!

Now the real fun begins. I have time to get back to restoring these venerable old machines.


I plan on (re)starting by restoring one of the non-working machines. I'll start with the keyboard which is totally dead except for the U/C light that stays lit.

Keyboard Restoration

Bryan Blackburn has a page devoted to Keyboad Restoration which has some very good tips.

Keyboard restoration is the most tedious, frustrating part of restoration. The process goes something like this:

1 - Disassemble keyboard cabinet
2 - Remove all keycaps
3 - Remove key plunger housings
4 - Carefully remove all foil
5 - Clean everything
6 - Fabricate new foam pads
7 - Glue foam pads to key plungers
8 - Test each plunger
9 - Reassemble

Sounds easy doesn't it? Perhaps this is a good time to talk about patience. Restoring a keyboard can take lots of time and effort.

(1) Disassemble Keyboard Cabinet

Remove all of the screws holding the aluminum housing in place and carefully remove the keyboard and the plate to which it is attached. Disconnect the 18 pin dip connector at the top left of the keyboard.

(2) Remove all Keycaps

The only way to remove the key caps is to gently (or not so gently) pull each cap off of the plunger by grasping the key and pulling up. There will be a spring behind each cap that maintains upward tension on the key when at rest. Notice that the often used keys like "return", "rub", etc. have a larger yellow spring than the other keys. This will become important during reassembly. If you do not have another keyboard to look at during reassembly, it's a good idea to take a picture of the assembled keyboard or take good notes of key position that can be referenced during reassembly.

(3) Remove Plunger Housings

The grey plunger housings are held on by two or three machine screws that go through the printed circuit board with a small nut on the rear of the board. Carefully unscrew each while holding the housing. Remove the housing and remove the white plastic plungers. As far as I can tell, other than the U/C button, it does not matter which plunger you use for which key, so organizing them is not important. It is however important to keep the plunger housings in the correct order. I always number the housings with a sharpie beginning with "1" on the lower right corner.

(4) Carefully Remove Gold Foil

You'll find that the gold foil backing can be very, very, very, very delicate. I've only seen one keyboard that had the foam backing in tact. If the foam backing is in tact and shows no sign of degradation (unlikely), you can skip steps 6 and 7. If you can easily pull the gold foil away from the plunger, it's probably a good idea to replace them all. You'll likely end up with a pile of gold squares with a dusty gray matter on the back side as pictured here. It's important to note that the foil backing must be in perfect shape to reuse. If you accidently break a foil, do not try to use it! At best the key may work just fine, but more likely, you'll get the whole keyboard back together then have a key or keys that aren't very reliable (argh!). If you do damage some of the foils, you can replace them with aluminium foil, but you'll change parts of the keyboard from capacitive to conductive which I'm not sure is a good thing!!! It does work, but I'm not sure of the future consequences. Did I mention patience? Be very careful with the plungers and foils as replacing either is next to impossible.

(5) Clean Everything

The gunk (glue and residual foam) can be scraped from the back of the plungers with your fingernail or an exacto knife. Be careful not to break the ears off of the plungers. After that, I dump all of the keys, plungers and springs into soapy water and clean using an old soft toothbrush. I've restored one keyboard that was exremely yellowed by cigarette smoke by using #0000 steel wool and lots and lots of elbow grease. The letter and numbers are molded into the plastic key caps so you can actually remove the outer layer of the keycap without ruining the lettering. Have I said anything about patience lately? This process can take many hours. I spent about 5 or 6 evenings with steel wool working on each individual key cap. The keycaps will not be as shiney as they were before, but the yellow stains will be gone...... Take this at face value. This was my experience, your mileage may vary....

After the plungers, keycaps and springs have been cleaned, be sure to rinse in clear water to remove all of the soap or cleaning solution, shake off excess water and place on a paper towel to dry. Now that you're finished with the easy part, it's time to move on to cleaning the foil

The foils are probably sitting in a pile with lots of foam dust falling all over you work area (see photgraph). I clean them in two steps; 1) using a soft toothbrush I gently hold the foil by one edge and CAREFULLY brush the foam residue off of the back side. I believe that Bryan Blackburn leaves the last of the residue on the foil as it helps strenghten the foil (and keeps it from curling up). Due to the nature of the new foam that I use, I've found that the residue keeps the foil from sticking completely to the new foam, so, I use acetone and lots of Q-tips to very carefully remove the glue residue from the back of the foil. And, yes, the foil will curl up and be very fragile following this step.

(6) Fabricate new foam pads

I've tried several materials to replace the foam and found that 3/16" thick, soft weatherstripping with adhesive on one side works well. Stay away from "mounting tape" as the backing does not "give" enough to conform to the printed circult board to allow the keys to work reliably. The 3/16" foam will give the keys on thekeyboard a very short stroke ~ 1/16". If you like a longer throw on your keys, use 1/8" thick foam instead. I cut sections about 6" long from the role of weatherstripping and carefully unroll the gold foils and place them on the sticky side, gold side up.

If you have damaged some of the gold foils, cut a piece of thin aluminium foil large enough to make replacements (plus a few extra) and stick it (shiny side up) to the weatherstrip. Cover each strip with wax paper pressing firmly to 1) assist in sticking the foil to the foam, and 2) stick the wax paper to the foam where it is exposed. The wax paper is important to keep the foil in place while round holes are punched in the center of each foil. Using a simple round hole punch available at any office supply or "Hobby Lobby", carefully line up the punch with the hole in the foils and punch holes in each foil. Remove the wax paper.

As I'm somewhat artistically challenged, and can't draw (or cut) a straight line without a ruler, I machined this handy "contact jig" from aluminium for the express purpose of cutting new contacts. It's exactly the size of the foils and is used as an outline by which to cut the foil and foam.

You'll also need about three or four new blades for your exact-o knive as this foam, paper, foil combination blunts blades pretty quickly. If you don't have the nifty cheater that I made, you'll have to use a metal ruler and or a steady hand to cut your foam. With this jig, I simply cover the foil, compress the foam completely and cut around the perimeter with the exact-o knife to get the foil to a square shape. Next cut the "edges" of the indention with the exact-o knive, finally cutting the inner edge with a 3/16" wide chisel or carving tool.

If I haven't mentioned patience lately, this is a good point. This is very time consuming, but care here will significantly cut down on reassembly troubles. Compression of the foam greatly assists adhesive effectiveness as well.

Cleaning the printed circuit board can easily be accomplished with a soft brush to remove dust and dirt. In addition, the contacts on the board should be cleaned first with an old fashioned pencil eraser then with a mild solvent (I use contact cleaner and carefully wipe off all of the residue).

I also clean all of the machine screws, nuts and small white stand offs replacing anything that is rusted or corroded.

(7) - Glue foam pads to key plungers

You should now have a pile of clean keycaps, springs, machine scres, nuts, plungers, plunger housings, and brand new plunger pads. At this point I usually layout all of the parts (except the new foil and foam pads) as they will be reassembled. I then line up about ten foam pads (gold side down) on a paper towel (I've tried wax paper with terrible results) and spray lightly with 3M general purpose spary adhesive. IMMEDIATELY (you'll have approximately 1 minute) AND CAREFULLY align and press the plunger face onto the back of each new pad. Be sure that the pad and plunger face are properly aligned or reassembling the plungers into the plunger housing will be very difficult. You can move the pad around on the face of the plunger slightly before the adhesive dries.

(8) Test each plunger

I like to be sure that each plunger/foam/foil combinaton will work before I reassemble. This can easily be accomplished by attaching the keyboard to your computer (yep without the keys!), loading basic, and carefully touching the face of each plunger to one of the silver pads on the printed circuit board. You should see a character appear on the screen. If not try rotating the plunger 90 degrees and try again. If none of the keys work, you may have other problems, not related to the plungers.

(9) Reassemble

Almost there..... Reassemble the plungers, housings, springs and keycaps one housing at a time, attach the housing to the pc board turn on the computer and test as each new housing or row are added. It's a lot easier to find a malfunctioning key immedately rather than when you get the entire keyboard back together.

If you've done everything right, you should now have a working keyboard......

Official dg keyboard documentation in PDF format.