Home Up Site Map Links Wish List Search

TV Typewriter

I am no longer active in this hobby for the foreseeable future. 
I will no longer maintain or update the website, but I will leave it accessible to the web for as long as possible (years).

 

Mark-8 Minicomputer
Apple-1
MOS Kim-1
V C F
Imsai 8080
Kenbak-1
TV Typewriter
LSI ADM-3A
ASR-33
The Digital Group

My Collection
HP-01
Test Equipment
Model Rocketry

Unreadable logo. The original, 
unreadable, 
digital group 
logo.

2003-11-13_dg_tvt001.jpg (175684 bytes)
172 KB

The digital group TV Typewriter

When the Mark-8 Minicomputer made it's debut on the cover of Radio Electronics in July of 1974, it drew the attention of an unusually large number of entrepreneurs. Within just a couple of months, newsletters had began, and companies started or moved to supply hobbyist with parts and information in the new field of personal computing. One of those moving quickly was Dr. Robert Suding, a founding member of the digital group. Among the first products designed by Dr. Suding to be offered by the digital group was a video card, as seen here, part of my TV Typewriter. This card was not intended as a stand-alone TV Typewriter so much as it was a direct addition to the Mark-8 itself. In an interview with Dr. Suding, he placed the date of these video cards in late 1974.

The video card has a total of 256 bytes of Intel 1101 memory. When I obtained the video card, I had little information on it, and I am thankful to all who emailed me and contributed bits of the puzzle. My card came to me missing a few chips, and looking a little rough. I managed to reverse engineer the circuitry and get the card operational just in time to receive a copy of the digital group "Packet #1", which fully describes the card, with schematics, and preceded the introduction of the card by a month or two. The packet also included other useful circuits and improvements to the Mark-8. Whoopee!! With the full information in hand, I built the TV Typewriter as shown here.
 

2003-11-13_dg_tvt002.jpg (149548 bytes)
146 KB
 

2003-11-13_dg_tvt003.jpg (139071 bytes)
136 KB
 

2003-11-13_dg_tvt004.jpg (151536 bytes)
148 KB
 

Construction

It took me quite a while to decide what to do with my video card. I did not want to add it directly to my Mark-8, as I wanted to preserve the Mark-8 in original condition, but did not have any alternative ideas that seemed acceptable. I also knew that I would want to use it with my Mark-8 in some way, since it was originally designed specifically for the Mark-8. After having plastic covers made for a few of my other machines, I decided to build a cabinet completely out of plastic. The challenge was to make it attractive and functional. The keyboard used was a complete unknown, picked up at surplus for an incredible price of just $2.50, and it is configured and labeled just like my ASR-33 keyboard, which I thought was a great bonus. I added lower case capability to the keyboard by a toggle switch on the rear panel, and the key pressed strobe has a selectable connection to the Mark-8 interrupt line via another rear panel toggle. This allows programming to handle keyboard operations through interrupts, a useful tactic for many applications.
 

The power supply is a modern day switcher chosen for small size and reliability. A required -9 volt input is supplied by a small regulator, visible in these photos just above the keyboard near the video card connector. The cabinet was built from my drawings by Hawkeye Plastics in Mesa, Arizona. They did a fantastic job. 

The monitor shown is a surplus item I picked up years ago. The housing was designed by me and made by Hawkeye plastics.

Operation

The operation of the TVT is a little clumsy and a bit off-beat. Although the keyboard will encode all of the standard control characters, the video card does not recognize anything but a "home" command. This means there is no cursor, no cursor functions such as a backspace , up or down movement, etc. Worst of all, no screen erase, carriage return or line feed! All of this must be implemented in software if it is desired! Otherwise, it works great! 

The screen shows eight lines of thirty-two characters per line. Quite small, but very usable. It is functional as a stand alone TVT by use of a jumper plug that fits into the output connector, looping the keyboard outputs to the video card inputs. It also plugs directly into my Mark-8 rear connector.
 

 

2003-11-13_dg_tvt005.jpg (146569 bytes)
143 KB

2003-11-13_dg_tvt006.jpg (149587 bytes)
146 KB

2003-11-13_dg_tvt007.jpg (224338 bytes)
219 KB

2003-11-13_dg_tvt008.jpg (237941 bytes)
232 KB

2003-11-13_dg_tvt009.jpg (208938 bytes)
204 KB
 

2003-11-13_dg_tvt010.jpg (207221 bytes)
202 KB
 

The TVT operates with only one quirk: it is a little slow, and requires a short delay implemented in software to update the screen without errors. This may be fixed by finding the slow chip in the memory bank, but I have no intention of changing any of the original chips at this time.

 

Photos of the Digital Group Video card used in the TV Typewriter

 

mark8_dg_tvt_02.JPG (3177730 bytes)

mark8_dg_tvt_04.JPG (3165308 bytes)

mark8_dg_tvt_06.jpg (3389792 bytes)

 

 


wordpress visitor

 
Unique Visitors Since 02/04

Copyright 2008 Bryan's Old Computers
Last modified:
October 16, 2009