micro-KIM decoder logic question?

[Michael]

Hi guys,

I'm looking at the I/O decoder logic for the micro-KIM schematic on the hansotten web site and I was wondering if someone could tell me if it's correct, please? With the U18 (74LS138) "A" input tied to VCC wouldn't that activate only the /Y1, /Y3, /Y5, and /Y7 outputs? I've got to be missing something. Can anyone help me out, please?

TIA. Cheerful regards, Mike

[GARTHWILSON]

Quote:

With the U18 (74HC138) "A" input tied to VCC wouldn't that activate only the /Y1, /Y3, /Y5, and /Y7 outputs? I've got to be missing something.

No, you're right. It should be the C input that is tied high in order to get the Y4, Y5, Y6, and Y7 outputs.

[Michael]

Thanks Garth.

Anyone know if there's a more up-to-date schematic for the micro-KIM?

Regards, Mike

[HansO]

Michael wrote:

Thanks Garth.

Anyone know if there's a more up-to-date schematic for the micro-KIM?

Regards, Mike

You may ask Vince Briel on www.brielcomputers.com

[Michael]

Hi HansO,

Just wondering if that's your web site? If so, can you tell me if there are there known problems with that schematic, Sir?

TIA. Regards, Mike

[HansO]

Michael wrote:

Hi HansO,

Just wondering if that's your web site? If so, can you tell me if there are there known problems with that schematic, Sir?

TIA. Regards, Mike

Yes, it is my website. The information there about the KIM-1 is coming straight from Vincent Briel, and there was a revision of the decoder logic. I am not sure that revision made it in the official documentation on the website of Vincent (the Microkim cd with the manual including schematic is on http://www.brielcomputers.com download section). Better check there and look in the forum discussions (around 2007 iirc).

Hans

[Michael]

Thank you, Hans.

You have a very nice web site.

I did search the Briel forums but I didn't find anything concerning the wiring of U18 (74HC138). Perhaps I missed it. The schematic on the micro-KIM CD seems to show the same wiring for U18 as the schematic on your web site.

I don't want to impose on Mr. Briel because I'm not one of his customers.

Cheerful regards, Mike

------<added>------

oops! just spotted the post at the top of one of the micro-KIM forum pages. Let me look at that...

Yes, that describes the design error for the "A" input on the 74LS138, which should be connected to A6 instead of VCC...

It's a shame that the "fix" didn't make it into the current schematic...

[vbriel]

Sorry about that, that schematic is not the production copy. Here's an updated copy.

http://www.brielcomputers.com/files/MicroKIM25.pdf

[Michael]

vbriel wrote:

Sorry about that, that schematic is not the production copy. Here's an updated copy.

http://www.brielcomputers.com/files/MicroKIM25.pdf

Thank you very much.

Cheerful regards, Mike