Port Expander Info...?

[Darrell N.]

daklein at netzero.net wrote:

> Does anyone know how a 'port expander' works?  Reading TH's file explains
> some of it to me, but does anyone have pink book sort of info about this
> sort of chip?  Specifically how what looks like a config register for it
> works.

If you are referring to the Motorola 68HC24 PRU (Port Replacement 
Unit) it is a chip that you add to an 'HC11 MCU that allows you to run in 
Expanded Multiplexed Mode (external RAM, ROM, etc address space) 
while giving you back the Port B and Port C pins that you lost to the 
address and data bus.  In other words, it allows you to run external 
RAM, EPROM, etc, but still retain all of the G/P I/O pins as if you were 
running in single chip mode.  

Motorola no longer makes this chip, but it is being second sourced by 
Tekmos.  (www.tekmos.com) If you want more info mail me offlist.  
There is also a 68HC11 mailing list at:

68HC11 at oakhill-csic.sps.mot.com

which you can sign onto and ask any HC11 related questions. 

BTW, who is "TH" and to what file are you referring?


darrell n
Calgary, Alberta, Canada
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