![[?? Elf II]](elfII_01.jpg)
Most recent revision of this page Sept 19 2024(c) Herb Johnson. Some photos and text
(C) Will Dotson used with permission. This Web page introduces the Elf II I obtained
from Will Dotson. Work in progress figures out his modifications and is on another Web page. Check the other ELF II I worked on (don't own) at this Web page. Web search will find many pages on my site about the 1802 COSMAC, including the Lee Hart
1802 Membership Card pages - Herb
In late July 2024 I obtained this Netronics Elf II system, delivered by the owner and original builder Will Dotson, who was local to me. Notible is the ELFII to S-100 interface he designed, but also his mods to various cards, and an LED-array driver card Will designed himself. This work was quite an achievement in the mid-1970's, and as Will tells me it was from various 70's surplus or common electronic parts. It's commendable to have constructed, modified, and operated microcomputers like these, back in that era. So I'm inclined to keep it largely intact. Below, I provide some background about Will's construction of this microcomputer, and some biography. - Herb
Most of these "delivered" photos are from the original owner, used with permission. They are a quick inventory of the items I obtained.
Elf II system with ASCII keyboard.
Netronics Professional ASCII keyboard.
ASCII keyboard from the back. I don't think this has video?
But there's two boards + keyboard inside the ASCII kbd case
Elf II with plex case and five boards in place.
Boards from rightmost at the keypad, to case edge are:
1) LED interface board. 2) ROM board. 3) 4K RAM board. 4) 16K RAM board. 5) ACI "giant board". The S-100 interface is not installed. Here's a view from the other side, boards in reverse order.
LED interface board, 18 IC's, created by Will Dotson.
LED interface board, back. My photo.
a processed photo of the LED board's ICs
ROM 2716 board, etched by Dotson.
- there's five IC's and eight 2716's. No docs but I'll figure it out.
back of ROM board
Netronics 4K RAM board of 2102's
back of 4K RAM
16K static RAM board, 6514 B3261 1K X 4 CMOS
- This is slightly different from the Netronics 16K 2114 board. It's also hand-etched.
back of 16K board
Netronics ACI-1 "Giant board"
back of ACI-1 board
S-100 interface board not installed, loose
- connector on cable plugs into Elf II as bus extender. Board is S-100 bus master.
back of S-100 interface board
Will uncovered this S-100 backplane and sent it to me in late Aug 2024.
top of S-100 backplane the S-100 interface board plugs into this. Connectors are too close together, about 1 cm or 3/8" apart
back of S-100 backplane Wirewrap S-100 connectors, soldered with bare wires
S-100 backplane wiring Insulating plastic woven through the wirewrap pins, to allow bare-wire connections with successive bus pins without touching the adjacent or nearby bare pins. I've never seen this method, very clever. Bill says "I bought
it (apparently for $5) at the Trenton Computer Festival around 1980."
Decoding the various mods made by Will Dotson is on another Web page.
Boards in chassis, keyboard:
Elf II ASCII keyboard docs
Elf II keyboard schematic photo
Elf II video display board doc photo
Elf II power supply docs (p/s not available).
Elf II (console) docs
Tape Controller docs photo
LED inteface custom, photo of partial schematic
bus boards:
LED interface (custom) board, docs as described
2716 ROM board, no docs
Not photographed: 4K Memory board docs, Netronics docs
fragment of 16K RAM docs photo
- board should not be hard to figure out.
ELF II ACI-1 Giant Board doc photo.
S-100 interface docs photo
I'm decoding the various ElfII mods made by Will Dotson. I show my findings on another Web page. Meanwhile, here's some notes on the various bus boards. - Herb
The ElfII in chassis: I have some Netronics docs from my previous Elf II work.Some of these docs are on Web archives. But the copyright owner still asserts certain rights; so I'll not put actually document scans on my Web pages. Contact me if you need a document, or check around the Web. A particular feature of Will's ElfII is a small modification board, under the ElfII backplane. I sorted out the circuit,details on another Web page.
LED interface board: Designed by Will Dotson. This board has quite a lot of logic, 18 CMOS ICs. It's hand-wired and soldered. Will Dotson found a partial schematic after I obtained the system. Will then described the board, his notes are below.
ROM board: has five IC's driving the 2716's. Two CD4050's hex buffers non-inverting. one 74LS373 8-bit latch. one 74LS00 (quad NAND gate). one 74LS138 3 to 8 decoder. Should not be hard to reverse-engineer. Will hand-drew the circuit layout, looks like photo-resist.
power supply: was not provided to me, but the Netronics product was a simple unregulated AC to DC supply. The paper docs describe this Netronics product. I'll see what I can come up with for +8V -8V power, maybe something looking like the original Netronics (if I can find a photo of it).
video display board: I'll examine the acquired docs later. This is in the ASCII Keyboard chassis. A Web search finds some information at Ed Keffee's site.
S-100 interface: It's not critical for Elf II use of course, but interesting. I have his schematic. It should not be hard to figure out. It's a bus-master interface so it "drives" the S-100 bus, for things like S-100 based I/O and maybe memory.
Here's Will's description from his July 2024 recollections and his look at the LED interface partial schematic he found. And here's a processed photo of the board to show the IC's on it. I'll add other documents when found or created. - Herb
more notes, from Herb: Here'a my sketch of the IC's and components. There's three 555 timers. Trimmer pots labled "display clock" and"interrupt rate" and "lockout mono-stable". There's a unlabled trimmer on a CD3130 which is a CMOS op-amp. The other IC's I can identify are 4013, 4023, 4093, 409?, 4023, 4020, 4001, 74C193, 4049, 4001 - more than one of some. - Herb
notes from Will Dotson: I'm surprised there was no diagram of [the LED board] in the folder [I provided], but I think I've located it. A picture of the diagram [was emailed to you]. I think you might not find this board to be particularly useful, although maybe it could be modified to be so for someone. It was designed specifically to interface to my 32 x 32 LED display panel. The details of how it worked are a little hazy now after all these years, but here goes:
You noticed what looked like a four pin connector on the board, and it is. It's what's known in the R/C world as a 4 pin Dean's connector, and it's used mainly for servos in R/C planes. (I have the male ones if you'd like one.) This was the interface to my display. In addition to ground, there is a clock signal, a data signal, and a frame signal. The frame signal was the interrupt rate, usually set at about 10 frames per second. The clock was about 1024 times that, or about 10240 Hz. The data was a level at each clock edge.
[On the display incoming data] I used latching shift registers, but no, I did not use any error checking. It never was needed with direct wire, and we never got the thing airborne [on the blimp we came up with, or to save the data] with a tape drive. If we had, and IF we experienced too much noise, then I would've had to figure something out I guess [The order of the data was] "raster style", left to right, top to bottom.
At first I simply wrote code to implement these signals, but later I used a DMA scheme. The frame signal would generate an interrupt. The interrupt code would generate a DMA request to the CPU. As I remember there was some kind of direct DMA support in the 1802. Remember, this is all very hazy [years later]. The idea was to use a scheme that could be recorded easily on tape (but I never got that far.)
I had written a primitive graphics editor for the display. There was a blinking "cursor", one of the LEDs that I could move to any LED on the display. Then, I could turn on or off any led to form a "picture". That picture would occupy the first 128 bytes of the memory allocated to the display, which was really all RAM in the system that wasn't already being used for something else. I wrote functions to do things like drawing lines, printing text in different sizes, shift the picture in all directions, etc. etc. Then I could increment to the next frame and do it all again, eventually making an animation. Playing back the animation was done by stepping the DMA pointer on each interrupt.
Later I bought an old security camera (still tube based) and made an interface for that to sample 1024 points 30 times per second and send it to the Elf.
I still have the LED display (which needs a few parts replacements now). I later used it with my CP/M system and even later with my IBM PC type system using a parallel port. We don't have parallel ports anymore, so I will someday have to get one of those USB to parallel thingies if I want to play with it.
I wrote all my 1802 code in hex, and I still have it all, on paper. I would just put circles on the page where address info should go, and then count manually and fill them in. I did eventually learn how to "write" an assembler using Microsoft's MASM with macros. I think I used this method with the 1802 a little, but I certainly used it to write 6800 and 6502 code.
Is there anything else on that board? I'm not sure, but I did notice a 3130 dual op-amp. Could that be something to do with sound? I don't know. - Will Dotson
Software docs:
top to bottom: Netronics monitor, cass assembler. Netronics
copies of Tiny BASIC (Pittman) & User docs
Not shown: Tiny BASIC modifications note
Cassette editor and light pen docs photo
- no light pen provided but they are not complicated.
In the mid to late 1970's, before CP/M with floppy drives on 8080/Z80 systems, people operated these cassette-based systems, particularly with the COSMAC 1802 processor. Will worked with components from surplus stores and by mail-order, and bought kits from Netronics and others. Some etched their own copper PC boards, using photoresist to transfer circuit board layouts bought from kit companies or sold through magazine articles. Or they hand-drew their own circuits with a "resist pen". Or, they wire-wrapped. All these methods were used with this ELF II.
As Will Dotson told me, he lived in the NYC area in the 1970's, and became interested in digital electronics as microprocessors emerged. There were plenty of surplus electronics shops on Canal Street and adjacent in Manhattan. Their low prices suited his very modest income at the time from woodworking and cabinetry. Web searches on "surplus electronics Canal Street" will give one a flavor of surplus shopping there and in other surplus companies around the USA in the 70's and later. Loss of US manufacturing, the emerging Internet, and unrepairable digital electronics eventually ended most surplus companies into the 21st century.
Meanwhile, Bill learned microprocessor assembler, to program processors to drive things like homemade LED arrays (the board driven by the ELF II, and by later computers). His searly experiences with microcomputing and assembly language and BASIC, later got him programming jobs and a long career in IT support for portable computing (Tandy model 101's, later desktop MS-DOS PCs) and in IT mainframe computing. That was not an unusual story from the microprocessor era. Will describes the blimp he and his friend Bill Samson built on that linked tribute Web page. - Herb Johnson
Will described his transition into S-100 and CP/M: "I built a homebrew CP/M system using mostly stuff I bought at various Trenton Computer Fests. I had little money at the time, so I did a lot of crazy things, like repurposing an SMS Z-80 card that was built for Western Union by sawing off the edge connectors and glueing on an S-100 one. Then I wired the connector to the board. I managed to figure out how to map the signals without a schematic of the SMS system. I'm not even sure I could do that now. I recently sold that S-100 system on eBay." - Will
Copyright © 2024 Herb Johnson
