A quick check of the datasheets shows that the only difference is pin 14
which is a second chip-enable line on the smaller device, whereas it's the
most significant address bit on the larger device. The Syntor can address
either the smaller or bigger part depending on jumpers. If your radio was
previously using 256x4 PROM's, it should have pin 14 jumpered to ground
already, just program the lowest 256 nybbles of the larger part and it
should work fine.
I took a quick look at the Syntor schematic - you should be able to use
devices that aren't tri-state since the Syntor "shuts off" the PROM when
it's not being read by removing Vcc. A 74S387 (a non-tri-state version of
the 82S129) is half the price at Jameco - $3.95. I didn't check an MCX100
manual, but I'm guessing the circuitry is similiar.
BTW, if you're tempted to buy some of those parts (or their cross-referenced
cousins like 74S287's) from offshore eBay sellers, caveat emptor. I bought
a batch of 74S287's from an eastern European country and they passed
blank-test but every one of them gave an over-current fault when trying to
program. I think three other programmers were tried aside from my BP Micro
and all had the same result.
--- Jeff WN3A
> -----Original Message-----
> From: Repeater-Builder@yahoogroups.com
> [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Kris Kirby
> Sent: Saturday, December 05, 2009 3:22 PM
> To: Repeater-Builder@yahoogroups.com
> Subject: [Repeater-Builder] Syntor/MCX100 Prom question
>
>
>
>
> I have a VHF Syntor and a few UHF MCX100s. I'm looking into
> purchasing
> PROMs to program them with. The UHF MCXs had the knob-stop
> removed and
> it now turns to all 16 positions, however the Syntor is bare
> and may be
> strapped for a single frequency.
>
> Jameco lists the N82S129 (256x4) for $11, and the N82S131 (512x4) for
> $8. Can I buy the larger one (cheaper one) and fill it with
> FFs or 00s
> and have the radio operate correctly?
>
> Since they are PROMs, I only have one shot per device, and
> I'd like to
> keep this a cheap project. ;-)
>
> --
> Kris Kirby, KE4AHR
> Disinformation Analyst
>
>
>
>
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> Date: 12/05/09 08:13:00
>
>
>
