Back Porch circuit and a back porch generating ULA

Discussions about Sinclair ZX80 and ZX81 Hardware
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bola_dor
Posts: 120
Joined: Wed Oct 02, 2019 5:32 am

Back Porch circuit and a back porch generating ULA

Post by bola_dor »

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.
20200521_211818.jpg
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?
20200521_211624.jpg

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1024MAK
Posts: 2890
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: Back Porch circuit and a back porch generating ULA

Post by 1024MAK »

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

Mark

stroebeljc
Posts: 31
Joined: Thu Apr 23, 2020 6:02 am

Re: Back Porch circuit and a back porch generating ULA

Post by stroebeljc »

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?
John

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