Talk:MOS Technology SPI

74'639 and '245 are not substitutes

I have replaced the (anonymously contributed) paragraph claiming that the 6829 is the same as a 74'639 with a paragraph describing the differences. I have removed the paragraph claiming that a '245 can be substituted in "input" applications because it is not the case that input applications never need pull-ups. (Any application may or may not need pullups and, for an application that does, the 6829 may have been chosen specifically because it provides them.) Also, that section was wrong in the C16 being an "input" application; my own personal check of the ROM code indicates that the 6829 was used for output, and the TED was read for keyboard input. Cjs (talk) 01:53, 20 May 2022 (UTC)

It might be worth investigating what is needed to replace a 6829 in the Commodore 16. forum.6502.org has a thread on this that may be helpful. I also know of a board specifically designed to be a replacement; I'm working on getting a source for this. Cjs (talk) 01:53, 20 May 2022 (UTC)

6829 latches output state

Looking more closely at how the C16 keyboard interface works (my work on this is not yet published), it seems clear that the 6829 must differ significantly from the 74'639 in that it also must have a latch for the output state, though this is not mentioned in the data sheet. (Without this, C16 keyboard scanning could not work.) I intend to fix this once my work is published. Cjs (talk) 00:40, 23 May 2022 (UTC)