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From:
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[email protected]] On Behalf Of Lee Hart
Sent: Friday, April 30, 2021 12:04 PM
To:
[email protected]Subject: Re: [Z80MC] SD I/O 1.8MHz resonator
Zanchius wrote:
Good morning all,
This is proving to be another hard to find component, so I got a 2MHz
one instead. If I understood correctly there's a direct correlation with
the terminal baud rate provided by the UART. Would 200KHz make much
diference?
Hi Flavio,
Yes, I'm having trouble getting the 1.8 MHz resonators as well. Mouser
quit carrying them, so I bought my last batch from Tayda2009 on ebay.
But they seem to have gone out of business. As for the FJN3303 and
FJN4303 transistors, I have enough for customers; but shipping to the UK
is expensive.
The frequency is critical to get the right baud rate. Changing from 1.8
to 2.0 MHz will change the baud rate from 9600 to 1066 baud. It will
still work if you can set your Terminal program for such an oddball rate.
A better solution is to get a 1.8432 MHz crystal, which is a standard
frequency and fairly easy to find. Crystals don't have the internal
capacitors, so you'll also need to add two 20pf capacitors, one from
each side of the crystal to GND (the schematic in the manual shows these
capacitors).
Another option is to change the divisor in the 8250 UART. This can
compensate for your 2 MHz resonator. But it means changing a byte in the
EPROM, and burning another one.
Lee
--
A designer knows he has achieved perfection not when there is
nothing left to add, but when there is nothing left to take away.
-- Antoine de Saint Exupery
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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