Sinclair ZX80 / ZX81 / Z88 Forums

Posted: **Fri May 22, 2020 2:56 am**

Hi,
I've built the 555 based circuit By Ziggurat http://zx.zigg.net/misc-projects/
I plan to use it on a ZX80 but meanwhile tested it with my CZ1000.. with a Ferranti 2C210E ULA which grates an appropriate back porch.

What I've noticed is a really crisp, steady and noiseless K cursor but with a black left border.. is this because the preexisting backporch added to the new one or did I messed up something?

Posted: **Fri May 22, 2020 2:51 pm**

A longer black porch will eat into the left hand side border...

Mark

Posted: **Sat May 23, 2020 3:46 am**

You should be able to reduce the duration of the back porch by changing the RC values on the 555. Of course, then it may not work so well on the older ULA. Maybe a way to switch in different R values?

Sinclair ZX80 / ZX81 / Z88 Forums

Back Porch circuit and a back porch generating ULA

Back Porch circuit and a back porch generating ULA

Re: Back Porch circuit and a back porch generating ULA

Re: Back Porch circuit and a back porch generating ULA