Understanding STK500

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Hi Freaks,
I was looking at the STK500 schematic and wondered how the different IC's are multiplexed?

I saw that all the similar function pins from the different sockets (e.g.port A,B,C,D pins) are bussed together and labeled as PAT[7..0] etc.

Here is a stupid question: If there are more than 8 pins of say port A multiplexed, why is it labeled as PAT[7..0]? Is it just the standard 8 bit bus notation?

Also I saw on sheet 7 that say, the port A pins are separated and connected to J702,J706,etc. Are these switches? Then they are connected to J700 on both sides. Why is that?

I would greatly appreciate it if any of you has seen a detailed circuit explanation of the STK500 schematic. I did search on the forum and found Colin O'Flynn's notes on repairing an STK500 but it does not go into details of this multiplexing of different AVR's.
Thanks for your patience.

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Quote:

If there are more than 8 pins of say port A multiplexed

An AVR port never has more than 8 pins. And I'm not sure I would say that the pins are multiplexed.

Quote:

the port A pins are separated and connected to J702,J706,etc. Are these switches?

No, they are the pin headers (the breakout headers). If you read not only the schematic but also the component placing PDF this will become much clearer. (The "J" prefix for components are usually used for headers and other connectors in schematics.)

Quote:

Then they are connected to J700 on both sides. Why is that?

Continuing in the same vein, J700 is one of the expansion headers. (The left one, with the STK500 orientated for normal use.)

In essence, eg PCT3 is a signal line that is connected to several things (eg a pin on each of the target AVR headers, the breakout header, the expansion header...). PCT[0..7] is just a notation for several, in this case very similar, signals bundled together because you want to "distribute" them together - the concept of a signal bus.

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Also you should review the STK500 User Guide. It will describe the board in detail and includes a block diagram near the rear of the doc file.

Also be aware that there is an STK501 which adapts to it to support larger chips such as the Atmega128

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There are in fact quite a few daughterboards for the STK500. See the AVRStudio help file.

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Multiplexing is not an issue because only one processor position can be filled at any time.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Thanks,Johann that helps a lot.

Yes, I have the STK501 as well. I was just curious if all those floating lines (the ones which will not have a processor plugged in) can cause problems such as noise, signal integrity etc.