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http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

Or... you could eliminate the transceiver IC and just have a header with the TTL level signals. Then simply plug in a USB-to-TTL Serial adapter or an RS232-to-TTL Serial adapter...

I still have a bag full of little circuit boards that fit inside a DB9 connector & hood for the RS232-to-TTL adapter shown below...

Cheerful regards, Mike

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

Thanks, I noticed that on the datasheet, but I didn't see the 232a on mouser, I'll look again though, because that could save some space.

In other news, I've been considering a monostable circuit for driving RDY low when talking to the EEPROM. My plan is to drop it for 150ns, which should be enough time for most EEPROMs (a couple take 200, but I'll stay away from those). I found this AHC series IC that seems to be right for the job. If my math is right, I'll need a 10pf cap, and a 3.3kOhm resistor to achieve 150ns. (I originally was planning >1000pf cap to keep it simple with a k factor of 1, but there's a note in there stating to be careful with large value caps, as they can damage the chip if the power supply cuts off too quickly, so instead I went for the smallest cap possible, and a k factor of 4.5)

I suppose the adapter is probably just as complex as what I have on the board...this may be something I need to consider, although I would like to have the port on the board, I feel like it's a more solid connection than what I could do with TTL (I'd probably use pins for something like that, because another port wouldn't save me much space over what I have going right now)

I always use TTL level for my UARTs, using 3 pin Molex

I may really need to look into getting -12v on the board. I saw your "non-standard power supplies" in the circuit potpourri, and I'm resistant to it only because iirc it uses a lot of discrete components (diodes I believe) that would take up quite a bit of space. Plus, having the max232 do it for me makes my job a bit easier on the design side, although as you say, the line drivers provide a layer of protection since they're mostly bullet proof.

Something I asked a while ago and just remembered it never got answered, I have the CTS and RTS connected for the USB-TTL header, through resistors like the Rx and Tx lines, my assumption was this would give me hardware handshaking on it, but I seem to remember that...Daryl's? page didn't use those lines for the usb-ttl header.

Can I use these lines? Will they provide hardware handshaking?

Something I just realized is, if I use a monostable circuit for RDY generation, I can use a variable clock and be fine, since the clock won't be changing to access the EEPROM

does this sound feasible?

RDY needs to be synchronized to clock, though

It does? that's a bummer, I thought that it would just continue at the next PHI2 high transition

Signals like RDY go inside the CPU and are then distributed to dozens of different flip-flops, all switching on the same clock.

If RDY is allowed to change at any time, then it could change at the same as the clock, and some flip-flops would then see it as '0' and others as '1' due to small variance in timing and thresholds.

ah, well I suppose I can still wait state on the variable clock though.

The name of the game here is saving wait states, because I don't think 2 is adequate at 20Mhz operation for 150ns eeprom, and I'd like to use only a single dual flipflop chip.

I may look at some NVRAM that has 70ns access time

You could use asynchronous delay and then feed it through flip-flop to synchronize it.

I was planning on using the circuit that's floating around here on the forum that has 2 flip flops for 2 wait states, it's asynchronous trigger but synchronous wait states to clock

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?