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Old 7th Aug 2021, 7:06 pm   #91
Timbucus
Octode
 
Join Date: Mar 2019
Location: Barry, Vale of Glamorgan, Wales, UK.
Posts: 1,165
Default Re: MK14 Programming Interface

Quote:
Originally Posted by SiriusHardware View Post
So that means you need either 8 column optos or 8 row optos - maybe both, if you don't know in advance whether the target system needs to pull the lines up or pull the lines down.

Also the polarity matters, so you need to cater for the possibility that the target system might have a large number of driven lines and a small number of read lines, or a small number of driven lines and a large number of read lines.

It might also be useful to have up to two additional undedicated optos (like the reset opto, the output of which is not specifically connected to anything) - these would be for connecting straight across the CTRL and SHIFT keys on an alphanumeric matrix keypad, so that the uploader could press one of these keys at the same time as pressing any other key on the keyboard via the more usual row / column joining method.
Sounds good but, adds a lot of complexity - I just used some pullups on the little adapter board for the Triton - I used one of the Optos to source current and left three unused. I think we discussed how we could do it for things like the SCRUMPI and I am about to tackle it for the Cosmac Elf and also the 77/68 that has just joined the project pile.
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