I started using this MCU in 2001, but quit when they indicated they were
changing the silicon and the specifications because their FLASH process
wasn't fast enough to support the then-advertised 50 MHz clock rate. I've
also used the 24.576 MHz input clock albeit divided by 2, since many
communcation frequencies fall out of that frequency, and have found that
with a 4x multiplier, resulting in a system clock of 49.152 MHz, one can
execute code quite reliably, both in Page Mode 1, from external program
memory, and from XRAM mapped into program space. That's near enough to the
original 50 MHz to make it interesting. I've not tried it with the current
silicon, however, so I don't know what it can do in current commercially
available hardware. You must make the change in clock multiplier part of
the code residing outside the internal FLASH, however, in order to ensure
you don't violate the specified limit.
In order to implement Page Mode 1, I initially used a very fast bus switch
to route the data from P2 to the address-low latch. I've found that a small
and fast CPLD is just as effective and less bother. I don't buffer the data
bus, BTW. I suppose that I could do that if I were to use a larger CPLD.
The bus switch is just that, a FET switch, hence it doesn't buffer the
signal. Of course, it doesn't add much propagation delay, either.
----- Original Message -----
From: "Adilson Oliveira" <adilson@...>
Sent: Thursday, December 01, 2005 4:34 AM
Subject: Re: [Sdcc-user] SDCC and DS89C420
> Matthew Smith escreveu:
>> Glad I'm not the only one!
>> Other than using sdcc_reg420.h to define your SFRs, you can just treat
>> this as an 8051/8052, just much faster.
>> I have to confess, I have only done some very basic experimentation with
>> this series. I had some problems due to the fact that I'd made a very
>> nasty breadboard for testing. I have since designed/etched/drilled a
>> PCB but have to do it all again as I discovered that I'd used the wrong
>> width SOIC package for the MAX232...
>> For specific information on these devices, Dallas has a forum where
>> you can post your questions. Just make sure that you specify your
>> device clearly - people tend to assume that you're using a DS80C400...
>> What OS are you developing under? If, like me, you are "penguin
>> powered", there is no "official" loader software (mtk) available at
>> present. There is, however, an "unofficial" one, dsmtk.
>> One final note - choose your clock speed with care, otherwise you may
>> have trouble loading your software. The good folks at the Dallas forum
>> suggested that I'd be best off working with a 24.57MHz crystal.
> Hi there.
> Nice to know that someone else is using it.
> Yes, I'm a linux guy. I'll check dsmtk. I'm aware of the clock issues.
> I've benn using these little fellows for some time already but with
> Thanks for the tips.
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