Kaypro II Green Screen Analog monitor

Trevor dePommeraie

Hi! I'm new to the forums, to the propeller, uCs, and electronics in general. I've recently acquired a Chameleon board and have been slowly teaching myself on it's application. I was looking at my old half-functional Kaypro II the other day and decided that I'd like to add the propeller to it.

On looking at the schematics for the Kaypro mainboard, I found that the internal monochrome green screen monitor is analog with NTSC compatible horizontal and vertical sync. 15kHz hsync, 60Hz interlaced refresh. The connector to the mainboard has pins for separate hsync, vsync, and video signals. I've tried a basic LM1881 circuit with no luck in getting a picture. Just connecting a composite source to any of the pins results in a nasty buzzing noise that doesn't sound healthy for any of the hv components in the monitor. I was wondering if anyone had any ideas that could help me out with driving this monitor. Could all of the needed signals be generated in the prop? Is the sync separator chip necessary? I've been reading the forum for a while and have been impressed many times by the vast wealth of knowledge that all of you display on a regular basis here.

The best online reference to the Kaypro II monitor that I've found is: www.ccs.neu.edu/home/bchafy/kp/kaypro.html

This guy has interfaced the monitor to a pc vga card by modifying the card's vga bios to produce 15kHz sync instead of vga sync.

Thanks in advance for your help!

Edit: Added Kaypro II mainboard schematic. Unfortumately, I don't have one for the monitor.

Post Edited (Trevor dePommeraie) : 3/11/2010 3:08:16 AM GMT

kwinn

Yes, the prop can generate all those signals although you may not be able to drive the monitor directly from the prop pins. you will need to buffer them. This may be as simple as a 5V cmos gate or a few transistors. I don't recall what the exact setup was on those monitors.

Trevor dePommeraie

Hmmm... That's something I hadn't thought of. I have heard of some old monitors being referred to as "TTL" monitors. Does this mean that the signals Will be represented over the TTL voltage range?

kwinn

Yes, a lot of the old monitors were driven by TTL levels for sync and video. I took a look at the schematics you posted (sorry, missed them the first time) and that is what the kaypro uses. The kaypro video circuit outputs 3 TTL level signals - Vertical sync, Horizontal sync, and Video.

It is no problem for the prop to interface to TTL or 5V CMOS logic, all that is required is a 2K2 resistor between the prop pin and the 5V chip input. A single quad or hex gate would do the job.

The video memory consists of 4 2114 1K by 4 bit chips arranged as 2K x 8 bytes. There are 5 counter chips in the video generator.
U1 (74LS161) which is clocked from a 12.9776MHz crystal
U6 (74LS393) which is fed from the output of U1 is the column counter (7 bits) which counts the 80? character columns across the screen and generates the vertical sync signal.
U3 (74LS290) which is fed from the output of U6 is the 4 bit character row counter, which counts the number of rows in each line of characters (5x7 character in a 6x8 block)
U14 (74LS74) and U11 (74LS393) fed from the output of U3 is a 5 bit counter that counts the number of character rows down the screen (24?) and generates the vertical sync signal.

U43 is a 2Kx8 eprom used as a character generator to produce a (5x7?) character in a 6x8 cell
U42 (74LS174) latches one row of 5 pixels for mux U41 (74S151) to present 1 bit at a time as the video signal.

Not sure if this is a 24x80 or 16x64 display.

Post Edited (kwinn) : 3/11/2010 5:26:28 AM GMT

kwinn

To summarize the above data:

Horizontal frequency probably 15.750KHz or 63.5uS period. Horizontal sync is about 10-15uSec of that time.

Vertical frequency 60Hz or 16.67mS. Vertical sync is about 1.2 - 1.5mSec of that time.

For interlaced scanning an odd number of scan lines is required - usually 525 is used. typically 21 or 22 scan lines are used for vertical sync leaving 480-482 horizontal lines for the image

Not sure what the polarity of the sync signals should be. Only 4 possible combos to try.

lynchaj

Hi!· I realize this is not exactly what you are asking for but is similar in some ways.· As part of a test for a new board we added a VGA display to a similar old Kaypro using a Propeller board.· Would this be a useable solution instead of driving the legacy monitor?

http://groups.google.com/group/n8vem/msg/a33de504e4240435

As I recall the Kaypro design (I looked into it closely while designing the N8VEM VDU since the Kaypro 10 also uses a SY6545 CRTC) their monitor circuitry is fed TTL signals·basically straight off the CRTC such as VSYNC, HSYNC, intensity, etc.· It is a very simple all digital interface.·

To drive the monitor with a Propeller, I would start with the Propeller TV driver but separate the VSYNC, HSYNC, and intensity signals into 3 separate lines and convert those to compatible signals.

The Kaypro is also nearly entirely 5V TTL so be sure to buffer whatever you send to it or bad things will happen to your Propeller.· To drive the Kaypro monitor directly, I would search for the TTL video conversion techniques.· This may be helpful

http://www.repairfaq.org/sam/vidconv.htm

Good luck with your project!· Thanks and have a nice day!

Andrew Lynch



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