{"id":2916,"date":"2025-01-03T14:10:51","date_gmt":"2025-01-03T14:10:51","guid":{"rendered":"https:\/\/elephantandchicken.co.uk\/stuffandnonsense\/?p=2916"},"modified":"2025-01-13T12:05:22","modified_gmt":"2025-01-13T12:05:22","slug":"lego-control-lab-interface-cable-woes","status":"publish","type":"post","link":"https:\/\/elephantandchicken.co.uk\/stuffandnonsense\/?p=2916","title":{"rendered":"Lego Control Lab Interface – Serial Cable Woes"},"content":{"rendered":"\n

Lego Control Lab Interface – Serial Cable Woes<\/h1>\n\n\n\n

If you have a Lego Dacta Interface B (AKA Control Lab or 9751) but don’t have the original cable, you might have trouble talking to it. The reason for this is that RX and TX are wired backwards compared to what you’d normally expect. Even more confusing, the gender of the RS232 port on the interface is female, which isn’t normally the case for this wiring.<\/p>\n\n\n\n

Getting the Right Cable<\/h2>\n\n\n\n

Buying an Original Cable<\/h3>\n\n\n\n

If you’re buying to connect to a standard RS232, 9 pin port on a PC, you’ll want Lego part number 9768-1<\/a>.<\/p>\n\n\n\n

If you’re buying to connect to a vintage Mac with RS422 ports, you will want Lego part 9769-1<\/a>.<\/p>\n\n\n\n

Lastly, if you’re buying for an Acorn Archimedes computer, you’ll likely want Lego part 9768-1<\/a> (the PC part).<\/p>\n\n\n\n

Making a Cable<\/h3>\n\n\n\n

If you’re making your own cable, you’ll need to keep in mind that the pinout of the port on the interface is described as follows in the manual :<\/p>\n\n\n\n

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The connector on the back panel is male and you only need the three pins shown to be connected for everything to work.<\/p>\n\n\n\n

Using a Null Modem Adapter<\/h2>\n\n\n\n

If you’re using a standard serial cable instead of one wired for the Control Lab interface, or using a USB to RS233 adapter, you’re going to need a null modem adapter, but one with a male plug on one end and a female plug on the other.<\/p>\n\n\n\n

Making Your Own Adapter<\/h3>\n\n\n\n

I made my own using two ribbon cable RS232 9 pin D Sub connectors from eBay. It is a little fiddly, but a fairly cheap solution. As mentioned above, the interface doesn’t actually use most of the pins (such as flow control) so you only actually need three wires.<\/p>\n\n\n\n

In your adapter, connect…<\/p>\n\n\n\n