CRTC chip

Dajgoro · Post by **Dajgoro** » Sat Aug 20, 2011 12:14 am

Hello!

Since i am building a 6502 project i wanted to have a color graphic module. So i found about the MC6847 CRTC color chip, and so i bought it on ebay. And i also had to buy the MC1372, and i did, on ebay. But there was a problem with the seller, and i never got the MC1372. So i asked a ebay seller who has all kind of old ic stuff, but he can't find it...
So i have two choices:
1. Have black and white graphic.
2. Get another color CRTC chip...

So does anyone know how could i replace the MC1372 chroma modulator chip with something other, or some other CRTC color chip that is similar to the MC6847 (i prefer PAL)?

GARTHWILSON · Post by **GARTHWILSON** » Sat Aug 20, 2011 12:51 am

Other 65-family video chips included:
6545 CRTC
6560 VIC (NTSC)
6561 VIC (PALB)
6567 VIC (NTSC)
6569 VIC (PALB) text
6572 VIC (PALN)
6573 VIC (PALM)

Dajgoro · Post by **Dajgoro** » Sat Aug 20, 2011 1:56 am

I can't find any of the on ebay, only one bit it costs 25$ with shipping(too much)...
The 6561 looks too good to be true, where could i get it?
Or anything helpful?

fachat · Post by **fachat** » Sat Aug 20, 2011 5:56 am

What out for the bus interface and the capabilities of those chips. The VIC 6560/6561 was built into the Commodore VIC20 - which had colour yes, but only 22 characters per line for example. The other chips have been used in the C64 and C128 (IIRC) and have been built for that specific environment. You may use them in other systems, but due to that history they have their peculiarities. The provide PAL resp. NTSC compatible (depending on the chip, the timing is fixed!) signals.

For a general purpose CRTC I use the 6545/6845 which has programmable timing and can thus be used for PAL as well as NTSC, but neetds more external logic, esp. if you want color.

André

Edit: the 6545 and 6845 are mostly compatible. See http://www.6502.org/users/andre/hwinfo/crtc/index.html

ElEctric_EyE · Post by **ElEctric_EyE** » Sat Aug 20, 2011 9:56 am

This might interest you. I bought 10 of them last year. They were Hitachi (HD46505SP) 6845 equivalents.

leeeeee · Post by **leeeeee** » Sat Aug 20, 2011 12:55 pm

Have you looked at thr Dragon 32 schematic?

That uses the MC6847 but doesn't use the MC1372 to generate the composite video.

Lee.

Dajgoro · Post by **Dajgoro** » Sat Aug 20, 2011 2:29 pm

ElEctric_EyE wrote:

This might interest you. I bought 10 of them last year. They were Hitachi (HD46505SP) 6845 equivalents.

The 6845 is not a complete video generator, it only provides video address...

And i can't find the dragon 32 schematic...

BigEd · Post by **BigEd** » Sat Aug 20, 2011 3:35 pm

See here and more generally here on worldofdragon.org

Dajgoro · Post by **Dajgoro** » Sat Aug 20, 2011 4:10 pm

I already found that, but it is impossible to read anything, too blurry...

Dajgoro · Post by **Dajgoro** » Mon Aug 22, 2011 2:16 am

Any other solutions?

Edit: I fount this chip:TA8759 on ebay, it looks complicated, might be of help.
The replacement chip for the MC1372 is the ECG855.

PontusO · Post by **PontusO** » Mon Aug 22, 2011 2:05 pm

Unicorn electronics lists MC1372 on their website, http://www.unicornelectronics.com/IC/MOTOROLA.html at a fair price.

Dajgoro · Post by **Dajgoro** » Mon Aug 22, 2011 2:17 pm

Minimum order 25$...

GARTHWILSON · Post by **GARTHWILSON** » Mon Aug 22, 2011 6:29 pm

Quote:

Minimum order 25$...

That's pretty common. Other ones will allow smaller orders but add an extra charge for them. Smaller orders just don't have enough profit in them to pay someone to take your order, fill it, pack it, the price of the box, the accounting, etc.. Just add some other parts to the order that you will probably need soon anyway.

Dajgoro · Post by **Dajgoro** » Tue Aug 23, 2011 3:37 am

I just submitted a order and i had to add a feeewwwwwwww more items, it will be for some next project...

Ok now lets assume i will use the Motorola mentioned in the first post, now i have seen there is a pin that disconnects the CRTC form the address bus, so it can be written into the memory. Does interrupting the address cause visible artifacts on the tv screen?

PontusO · Post by **PontusO** » Tue Aug 23, 2011 6:59 am

Yes it does,
You will either need to implement some sort of synchronization method that tells the CPU when it can write to the memory without causing screen disturbances. An interrupt caused by FS* is one way of doing that, polling FS* on a port pin is also doable but more expensive CPU cycle wise.

Another way of handling this issue is by implementing a double buffering scheme in hardware. You could have two SRAM devices separated by buffers, where you would always read and write into the SRAM that isn't used by the 6847 and then use a control bit in a register somewhere to simply switch the SRAMs.

I have tried both and the last one is more efficient but more expensive board area wise and more complex to design and build.