Re: TI-H: Replacing Capacitorr with Crystal?
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Re: TI-H: Replacing Capacitorr with Crystal?
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..)
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?
Matt Butch
>Date: Wed, 08 Jul 1998 20:45:11 -0400
>From: Bryan Rittmeyer <bryanr@flash.net>
>To: ti-hardware@lists.ticalc.org
>Subject: Re: TI-H: Replacing Capacitorr with Crystal?
>Reply-To: ti-hardware@lists.ticalc.org
>
>
>Actually TI wasn't at all sloppy. Quartz crystals are extremely
>expensive (just look in a digi/mouser catalog) whereas an RC pair
>is extremely inexpensive, especially when you buy 100,000
>resistors/caps at a time. There isn't any real reason for a precise
>timebase on a TI calculator anyway. I personally would have chosen
>a resonator just because they tend to be closer to the labeled value
>than an RC pair (capacitor tolerances being around 20%) but even
>a resonator would have been much more expensive than their SMD r/c's.
>
>Additionally, Quartz crystals are prone to shattering and I'm sure
>most of the students on this list have dropped their calculators at
>least -ONCE-. All in all TI knows what its doing...
>
>You can pretty easily yank out the RC combo and put in a crystal if
>you so chose, as long as there is an inverting crystal driver on
>the z80 in there. I'm not too familiar with z80 board design but
>I'd imagine it has two pins (Like the PICs/AVRs) for its osc, one
>to drive a crystal and the other as an input to its clock circuitry.
>Chances are the RC pair doesn't touch the crystal driving pin and
>just feeds its clock right into XTAL1.
>
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