Re: TI-H: Replacing Capacitorr with Crystal?
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Re: TI-H: Replacing Capacitorr with Crystal?
My TI-92 wouldn't work with my EII when I had pull up resistors on...
Gee... maybe its because I used an 8515... I don't know.
Btw, Bryan... E-mail me tonight. I've got some great additions and with
your help we can add them to the EII easily. Just need you to look at it...
>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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