Re: TI-H: Replacing Capacitorr with Crystal?
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Re: TI-H: Replacing Capacitorr with Crystal?
Matt Butch wrote:
> I know alot about the Z80 and designing boards for it.(Its my favorite
> microproccessor) Anyway, there is only one pin labled "CLK", it is
> connected to all devices that need a clock input, and connected to a
> anykind of of occalator(eg RC, occalating chip, crystal and associated
> components,ect, ect..)
Yeah, sorry. The MCUs I work with all have their own built in crystal
amplifiers, I forgot that the z80 is a 20 year old microprocessor
without such goodies.
> On another note I have a question regarding the EII, why do the data
> lines going to the TI-port have pullup ressistors and are also connected
> to diodes and to 2 more data lines. Doesn' the 1200 have internal
> pullup resistors? Didn't they source enough current?
I ditched the pullup/diodes about three weeks ago. The E2 actually works
pretty reliably without any pullups at all, but the firmware does use
the internal ones to ensure proper operation in all cases. Its not wise
to leave things potentially floating, in any case.
The pullup/diodes were a hold over from the Extender uP design, which
used a PIC.. the PICs have 'global' pullups that will pull up the entire
port, something that is clearly unacceptable. Using the d/r scheme also
prevents you from having to change port dirs... I was finding that the
PICs sometimes puke when you change pin dirs on the fly.
Its good to see at least some people on the list know their electronics
:)
--
Bryan Rittmeyer
mailto:bryanr@flash.net
http://www.flash.net/~bryanr/
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