{"id":8836,"date":"2018-12-27T08:35:17","date_gmt":"2018-12-27T13:35:17","guid":{"rendered":"http:\/\/www.willegal.net\/blog\/?p=8836"},"modified":"2018-12-27T08:55:45","modified_gmt":"2018-12-27T13:55:45","slug":"a-little-more-about-the-scelbi-scopewriter-interface","status":"publish","type":"post","link":"http:\/\/www.willegal.net\/blog\/?p=8836","title":{"rendered":"A little more about the SCELBI Scopewriter Interface"},"content":{"rendered":"\n

This interface is pretty simple. It uses the strobes and data bit 0 from three output ports to control the Scopewriter switches S1 through S3. It uses another strobe to load the character from the data bus into a 6 bit latch.<\/p>\n\n\n\n

\"Scelbi
Scelbi Interface Schematic<\/figcaption><\/figure>\n\n\n\n

I thought about how best to implement this design. I even went through the effort to create a PCB design.<\/p>\n\n\n\n

\"SCELBI
SCELBI Interface PCB<\/figcaption><\/figure>\n\n\n\n

In the process of creating this PCB layout, I think I found one mistake in the schematics. OS7 should be connected to pin 13 on Z5 instead of pin 4. I’ll verify this when I power up and check it out.<\/p>\n\n\n\n

When I remembered that I had a perf board with a 44 pin edge connector, I decided to build the Scopewriter interface with that. I could have etched the PCB that I laid out. This design requires a two sided PCB and etching those at home is quite a fiddly process. This perf board probably would have been slightly quicker to wire using wirewrap techniques, but I didn’t have a sufficient quantity of wirewrap sockets. I was able to complete the wiring on the perf board in about a half a day. That is about the same amount of time that it would take to cut, etch and drill a custom PCB. The result is shown below. <\/p>\n\n\n\n

\"SCELBI
SCELBI scopewriter interface<\/figcaption><\/figure>\n\n\n\n

The interface uses 22 signal lines, which doesn’t leave room for power and ground on the same side of the edge connector. I decided to add +5 volts and ground to pins 1 and 3, on the top side. Those are the red wires in the photo.<\/p>\n\n\n\n

Since I’m short on Amphenol sockets, I decided to connect three of the four strobes from the SCELBI chassis, without a full connector. I cut down and filed a finish nail so that it would fit snuggly into an Amphenol socket. Then I soldered it to the end of each wire.<\/p>\n\n\n\n

\"SCELBI
SCELBI Strobe Connectors<\/figcaption><\/figure>\n\n\n\n

It occurred to me that this interface could probably be redesigned to use two output ports instead of four. This can be done by latching data bits 1 and 2 with OS4, instead of using separate strobes to control S1 and S2. I decided to stay with the original design, so I could use the original software.<\/p>\n\n\n\n

The build decisions were partly driven by what I had in my spare parts stash, which once again proved diverse enough to support this project without requiring any new purchases. That is a good thing.<\/p>\n","protected":false},"excerpt":{"rendered":"

This interface is pretty simple. It uses the strobes and data bit 0 from three output ports to control the Scopewriter switches S1 through S3. It uses another strobe to load the character from the data bus into a 6 … 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-8836","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\/8836","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=8836"}],"version-history":[{"count":6,"href":"http:\/\/www.willegal.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/8836\/revisions"}],"predecessor-version":[{"id":8847,"href":"http:\/\/www.willegal.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/8836\/revisions\/8847"}],"wp:attachment":[{"href":"http:\/\/www.willegal.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=8836"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.willegal.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=8836"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.willegal.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=8836"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}