{"id":1272,"date":"2017-10-29T12:49:53","date_gmt":"2017-10-29T12:49:53","guid":{"rendered":"http:\/\/www.randomorbit.co.uk\/?p=1272"},"modified":"2017-10-29T12:49:53","modified_gmt":"2017-10-29T12:49:53","slug":"retrochallenge-201710-slow-progress","status":"publish","type":"post","link":"https:\/\/www.randomorbit.co.uk\/?p=1272","title":{"rendered":"RetroChallenge 2017\/10 \u2013 Slow progress"},"content":{"rendered":"

Well progress has been slow but thanks to some helpful and knowledgeable people (here)<\/a>, progress has been made.<\/p>\n

So what do I know now that I didn’t know before? Well, I burned a ROM that just tried to access an imaginary I\/O port. When I ran that and watched the _IOREQ_ line, I saw it going up and down which suggests that the program is running correctly from ROM. I put one of my screen-filling ROMS in that just access ROM and screen RAM and didn’t see any _IOREC_ activity so I think I can safely say that the processor is up and running.<\/p>\n

About a screen.<\/h2>\n

I wanted to see if the screen output I’m seeing is coming from video RAM or is being created on the fly by the hardware fault.<\/p>\n

\"\"<\/a>So I pulled out a video RAM chip. When I powered on the machine and reset it, the pattern on the screen was different to what I had seen previously. I took another RAM chip out as well and saw a different pattern. Each RAM chip on the Nascom-1 is 1 bit wide and so unfilled sockets will make the corresponding bit float high when accessed.<\/p>\n

I think this means that the video RAM is being read correctly or at least feasibly by the video circuitry.<\/p>\n

So now I’m looking at the memory addressing and swapping chips to see if the symptoms change. I’m also waiting for some spare 74LS chips to arrive so I have some contingency.<\/p>\n

 <\/p>\n

More soon.<\/p>\n","protected":false},"excerpt":{"rendered":"

Well progress has been slow but thanks to some helpful and knowledgeable people (here), progress has been made. So what do I know now that I didn’t know before? Well, I burned a ROM that just tried to access an imaginary I\/O port. When I ran that and watched the _IOREQ_ line, I saw it … Continue reading RetroChallenge 2017\/10 \u2013 Slow progress<\/span> →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_coblocks_attr":"","_coblocks_dimensions":"","_coblocks_responsive_height":"","_coblocks_accordion_ie_support":"","footnotes":""},"categories":[47,129,33,98,127],"tags":[],"class_list":["post-1272","post","type-post","status-publish","format-standard","hentry","category-c93-blog-posts","category-nascom-1","category-c84-retro-tech","category-retrochallenge","category-retrochallenge-201710"],"featured_image_src":null,"author_info":{"display_name":"andy","author_link":"https:\/\/www.randomorbit.co.uk\/?author=1"},"_links":{"self":[{"href":"https:\/\/www.randomorbit.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/1272","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.randomorbit.co.uk\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.randomorbit.co.uk\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.randomorbit.co.uk\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.randomorbit.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1272"}],"version-history":[{"count":2,"href":"https:\/\/www.randomorbit.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/1272\/revisions"}],"predecessor-version":[{"id":1275,"href":"https:\/\/www.randomorbit.co.uk\/index.php?rest_route=\/wp\/v2\/posts\/1272\/revisions\/1275"}],"wp:attachment":[{"href":"https:\/\/www.randomorbit.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1272"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.randomorbit.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1272"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.randomorbit.co.uk\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1272"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}