Yes, I started a blog about a new, for me, huge project: Building the Replica I.
Fortunatly I found that Vince Briel had released the assembler source for the Atmel ATMEGA chips to run the display and keyboard. I thought that finding the ATMEGA chips here in Denmark would be the greatest challenge, but hopefully yesterday I found a supplier, KOZ Electronics.
I might have been very naiv thinking, that if I could just find the components, everything would be fine. Afterall the computer would use standard composite signal.
Argh ... a composite signal is just not a composite signal. There's a NTSC signal and a PAL signal. I assume the Replica I will produce a NTSC signal.
Is there any way to change the firmware in the ATMEGA8 so it will send a PAL signal instead?
I might not worry so much after all.
I just connected my DVD-player to my composite monitor, and told it to use NTSC. It worked well. It was grayscale, no colors.
Who cares? The Replica I is not using colors, so it might work anyway, even though I only have a PAL monitor.
but what happens if you connect it directly to composite video into a PAL TV? That problem makes me think... I want to buy a replica, but I don't know if I'm going to see the image...
If I could see it in grey scales it would be ok, as you said about colours.
It seems that most TVs will handle the picture without colors. This doesn't matter on the Replica I, as it doesn't have any.
The main difference in NTSC and PAL is the encoding of colors.
There's also differences in lines pr. screen, but that's easier for a TV to solve than the colors. That's why most PAL TVs will work with NTSC signal in grayscale.
I have been told that it does work but the video on the replica is a simple 3 chip solution and every TV or monitor may look slightly different.
I have found that page: http://www.yoho-games.com/A_V_Accessories/VGA_Adapters/_TV_Video_System_Converter_(NTSC_to_PAL)/5241/product.aspx
Here is a cheap ntsc to pal converter... maybe it is a good choice.
first I'll try to connect the replica to a cheap b/w 5" Mx Onda TV I bought 2 years ago to use with my old zx81 computer (b/w output too, as replica). Maybe it works nice because colours don't mind and it can support 60 hz frequency. That last feature I realized time ago with a video games console, I put that on 60 hz and I could see nothing, but touching vertical sync image got perfect!!
But if at last it doesn't works, I'll try that converter
Thanks for your reply
The luma components of PAL and NTSC are the same except for there frame rate. PAL is 25 FPS and NTSC is 29 FPS. So you will get a black and white picture when using a NTSC signal on a PAL monitor or vice versa.
The chroma components are completely different so the monitor will just discard it.