As the proud new owner of a Saleae Logic-16, I did some tests using my two-board 65C02 setup and swapped between a standard 6551 (which works fine) to the new WDC65C51N chips (which don't). It's interesting... I'm quite certain there is not a problem with the hardware itself (decoding, data xfer, etc.). After the reset (used as the trigger) The 6551 is accessed after 2.3ms or so and initialized. On the 6551, both the RTS and DTR lines go low and the RxC line goes live outputting the baud clock frequency. After about 330ms, the 6551 is accessed again and data is sent out for a intro message (using SyMon III). You can see the initial bytes written to the 6551, then the TxD line goes active and steps the data out, followed by additional writes to the 6551 until all data is sent, then goes to input loop mode.
With the WDC chip, the initialization after 2.3ms works fine, chip responds and both the RTS and DTR lines goes low. However, the baud clock never starts and there's no clock signal present on the RxC line. After about 330ms, the same (initial pack of) data is written to the chip, but it never steps any data out on TxD (baud clock is needed for this, so no surprise), so things sorta come to a halt there, i.e., no additional data is sent as the chip is still busy.
In any case, the chip does respond to the code and part of it works (RTS/DTR) but the baud clock circuitry appears dead. I also used an external can oscillator.... with this (replacing the Xtal) you do get a baud clock out the RxC line after the initialization, but still no data is sent. Unless someone else can give me any other ideas, I think I have bad chips.
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Still, the simple fact that the baud clock will not run makes me suspect, unless someone could possibly come up with some logic as to why it doesn't run on the WDC chips but runs on all other chips. It is confusing I'll admit. Will post some schematics and pics once I get back home.
