{"id":8427,"date":"2017-09-26T22:01:17","date_gmt":"2017-09-27T02:01:17","guid":{"rendered":"http:\/\/www.willegal.net\/blog\/?p=8427"},"modified":"2017-09-26T22:11:19","modified_gmt":"2017-09-27T02:11:19","slug":"operating-an-original-scelbi-8b","status":"publish","type":"post","link":"http:\/\/www.willegal.net\/blog\/?p=8427","title":{"rendered":"Operating an Original SCELBI 8B"},"content":{"rendered":"

I recently spent a few hours with Mark Arnold and his original SCELBI 8B. This is the very machine that Mark used to develop SCELBAL with, way back, in 1975. Towards the end of our debug session, we had the machine in a largely working order! <\/p>\n

\"Mark<\/a>

Mark Arnold with his SCELBI-8B<\/p><\/div>\n

We spent a lot of time, troubleshooting what appeared to be an intermittent EPROM issue. Finally we discovered that that the edge connector on the EPROM board wasn\u2019t making reliable contact with the connector. After examining the board in detail, we noticed tarnish on the edge connector contacts. We used a soft pencil eraser to clean the tarnish off of the contacts and the intermittent operation completely disappeared. Fixing a computer with a pencil eraser was a first for me, though I expect others have done the same. Once the repair was done, Mark was able to reliably run a variety of MEA operations without any problems. <\/p>\n

With only 4K of SRAM installed, we were unable to load the full floating point SCELBAL, but we were able to load tiny SCELBAL using a simple bit-banged RS232 port. Once loaded, Mark successfully entered and ran some small BASIC programs. Weeks later, I understand that Mark still has the system powered on and it responds to MEA commands, without any need to reset or reboot.<\/p>\n

In order to declare that the machine is in 100% working order, a few things still need to be checked out. We had only 4K of SRAM installed, the other 8K should be added back into the system. We used a modified version of MEA with the page 76 EPROM changed. I created a version of page 76 EPROM with a 2400 baud driver, but we were having some issue with corrupted serial output characters. We don\u2019t know if that was a ground loop problem or a baud rate problem with the modified page 76 driver. Serial input at 2400 is working perfectly, but the timing for output is done differently, so it could be either.<\/p>\n

Finally, the cassette interface needs to be connected and tried out. I don\u2019t really expect any issues with that, as I have used that particular cassette interface with a reproduction SCELBI 8B, back when I was first troubleshooting my reproduction cassette interface.<\/p>\n","protected":false},"excerpt":{"rendered":"

I recently spent a few hours with Mark Arnold and his original SCELBI 8B. This is the very machine that Mark used to develop SCELBAL with, way back, in 1975. Towards the end of our debug session, we had the … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[16,7],"tags":[],"class_list":["post-8427","post","type-post","status-publish","format-standard","hentry","category-8008-scelbi","category-apple"],"_links":{"self":[{"href":"http:\/\/www.willegal.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/8427","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.willegal.net\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.willegal.net\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.willegal.net\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/www.willegal.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=8427"}],"version-history":[{"count":5,"href":"http:\/\/www.willegal.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/8427\/revisions"}],"predecessor-version":[{"id":8432,"href":"http:\/\/www.willegal.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/8427\/revisions\/8432"}],"wp:attachment":[{"href":"http:\/\/www.willegal.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=8427"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.willegal.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=8427"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.willegal.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=8427"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}