Modern expansion for VP-711 (CDP18S711) - Memory and GPIO

Joe Blackburn

We've seen a few projects with the Elf, and Ed Keefe's updates on the VIP II. And the Membership Card version.

Got me to thinking about a few things. I'd like to add modern tech in one or two boards to do the following:
32K RAM/ROM expansion
GPIO (similar to Elf2000) with PS2 Keyboard interface, UART or PPI, and with the addition of VT52 or VT1802 capability and 80x24 display.

Ability to use 80x24 output and keyboard at the same time as the 1861 and the direct composite output from the main board (text to GPIO, Graphics to composite output).
Several memory board designs exist for the VIP. To my knowledge, there are none that do the full GPIO part for the VIP.
This could be a single board with two connector tabs, that would slot directly into the VIP.



RAM- Use the Membership Card design as a guide.

GPIO- Both the Quest Super Expansion Board and the Netronics Giant Board have I/O ports.
Both are good examples.

PS/2 interface- Note that the PS/2 interface has some protocol to it. This means a specialized serial
to parallel converter or a custom bit-bang serial routine.

UART- The CDP1854 is easy to hook up and talk to. Other UARTs have been used. Modern UARTs
generally need some code to set them up. Better to use an older "dumb" UART like a 6402.
This will look to the COSMAC like a parallel I/O port.

 Note that little if any "consumer" 1802 software exists using a UART. It's all
bit-bang. Most of this was derived from RCA's old code as seen in UT-4 and UT-20.
Look also at Lee Hart and Herb Johnson's "IDIOT" monitor.
While RCA's approach was useful back in the day, it achieved very slow baud rates.
Recent work by David Madole (19.2Kbd.) and Chuck Yakym (at least 9600bd.) have
largely eliminated the need for a UART. These modern routines can be easily grafted
into older monitors,etc.

VT52, etc.- Bear in mind that smart terminal emulation is not simple; and probably
wouldn't run very fast on a COSMAC. You would also need higher video resolution than is
usually seen on COSMACs. Check out Todd's (taf123) work with the CDP1869/70/76 chipset
on his system. However, most video software used the 1861. Nowadays, however, the 1861
is extinct in the wild. Lee Hart and Chuck Yakym have developed a replica 1861 circuit
that is a drop-in replacement.

Consider using a PC term program on the VIP serial port.

Hudsonco1, welcome to the group!


Joe Blackburn

On Thu, Jul 11, 2019 at 08:32 PM, cmdrcosmac wrote:
PS/2 interface- Note that the PS/2 interface has some protocol to it. This means a specialized serial
to parallel converter or a custom bit-bang serial routine.

I think this adapter should work. It provides a choice of one of three outputs: 

"PS/2 Encoder interfaces industry standard PS/2 PC-compatible keyboards to devices requiring TTL-level RS232, parallel data , and/or PC XT signaling."

From what info I can gather, the RCA Ascii (Parallel) Keyboards are straight passthrough to Byte-IO Port of the VIP. 


This looks like it would do the job excellently. You would have to patch the monitor input code
to either poll an EF or use an interrupt service routine to watch the parallel strobe line.
As a bonus, you get a hardware UART (5V, not RS-232 levels) so you can use a PC term
program to load programs. Good find!
 Now if you want to go really old-skool, look into Don Lancaster's design in his
TV Typewriter Cookbook.


Joe Blackburn

Chuck - I believe the original VIP (CDP18S711) already has the routines for that in the monitor ROM. The diagram in the previous message is from the VP700 VIP Tiny Basic and VP-701 Floating Point Basic manuals. I do still have an old NISSEI Parallel Keyboard, but worried about age/condition, so changing to a PS2 Keyboard (which I have) seemed like a better option.

I think I may dial back expectations of "stuffing" this system, as I also have an ELF2000 with accessory cards, and an 18S604 based Development System in the 5-card chassis. Still collecting boards to expand that, but I have the 18S604, a UART card, and the digital display/control board, as well as a number of bare boards for memory, PROM Programmer, etc. I just thought it might be cool to max up the VIP.

But my main interest is in languages and programming, not games, so perhaps just adding the keyboard and memory to run the language options will do for that system.
The target system is an original COSMAC VIP, acquired in 1979. Back in the day, to use the Basic, you needed to up the memory in 4K increments to 20K. I'd like to replace the extra memory cards along with the expansion card that holds them, with a single card using 32K ROM/32K RAM.

I'm thinking of doing the Membership Card as well, which I checked out after your first note.

It's a shame Bob's not still selling boards/parts for the ELF2000, or I'd do more of those, for sure...