K
Hello,
It sounds like you guys are on your way to roughing a good spec and I am with you on most points.
I would ammend the following:
- 16 bit data bus
- 12 bit address
- Eurocard mechanical
Here are my arguments:
- I think having a full 16 bit data bus is much better. ISA supports this and it will make your scan time much faster. Most of your IO scan will be consumed by the processor waiting for the slow 8MHz bus, which gets really really slow with a lot of IO points. Basically you get twice performance for 8 lines cost. It can add up with high IO count machiens. Besides, most cards will be at least 16 bit, so you jsut got rid of one decoding operation!
- There should be many more address lines. 8 bytes is fine for simple IO, but not for analog IO, and complex plug in cards like motion controlers and non-vol cards. I suggest 12 bits of address so we can at least get up into the kilobyte range. The only reason NOT to go with more address is that it consumes more pins on the connector, which is not an issue (connectors aren't that much more expensive with more pin counts.) Keep in mind that you have a slot select for address decoding, so its not like you have to decode more address lines for simple cards. Basically you have a coupls 74AC latch chips for 16 bit output, and two 74AC bus transceivers for 16 bit input. When you read or write in the address range of the card the select line goes to the latches and reads/writes. Thats about as simple as they come.
- I really think we should go eurocard for mechanical. a eurocard is approx 3.8 x 6.5x 0.8 (inches). The hardware is really cheap if you buy the parts alone and assemble yourself. You can even get loads of prototype boards from places like vector electronics. You also get the benefit of having a whole boat load of power supplies that will fit in the same mechanical package -- if you so choose to want power in the cage.
I thihk it is important to build a strong and flexible spec so that we can get maximum use out of this across slightly different arenas. At the same time, keep it simple like it is so far. We don't need another PCI bus!! ) ::
~Ken
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It sounds like you guys are on your way to roughing a good spec and I am with you on most points.
I would ammend the following:
- 16 bit data bus
- 12 bit address
- Eurocard mechanical
Here are my arguments:
- I think having a full 16 bit data bus is much better. ISA supports this and it will make your scan time much faster. Most of your IO scan will be consumed by the processor waiting for the slow 8MHz bus, which gets really really slow with a lot of IO points. Basically you get twice performance for 8 lines cost. It can add up with high IO count machiens. Besides, most cards will be at least 16 bit, so you jsut got rid of one decoding operation!
- There should be many more address lines. 8 bytes is fine for simple IO, but not for analog IO, and complex plug in cards like motion controlers and non-vol cards. I suggest 12 bits of address so we can at least get up into the kilobyte range. The only reason NOT to go with more address is that it consumes more pins on the connector, which is not an issue (connectors aren't that much more expensive with more pin counts.) Keep in mind that you have a slot select for address decoding, so its not like you have to decode more address lines for simple cards. Basically you have a coupls 74AC latch chips for 16 bit output, and two 74AC bus transceivers for 16 bit input. When you read or write in the address range of the card the select line goes to the latches and reads/writes. Thats about as simple as they come.
- I really think we should go eurocard for mechanical. a eurocard is approx 3.8 x 6.5x 0.8 (inches). The hardware is really cheap if you buy the parts alone and assemble yourself. You can even get loads of prototype boards from places like vector electronics. You also get the benefit of having a whole boat load of power supplies that will fit in the same mechanical package -- if you so choose to want power in the cage.
I thihk it is important to build a strong and flexible spec so that we can get maximum use out of this across slightly different arenas. At the same time, keep it simple like it is so far. We don't need another PCI bus!! ) ::
~Ken
______________________________________________
LinuxPLC mailing list
[email protected]
http://lists.linuxplc.org/mailman/listinfo/linuxplc