Path: utzoo!attcan!uunet!pyrdc!pyrnj!rutgers!ukma!simon
From: simon@ms.uky.edu (Simon Gales)
Newsgroups: comp.sys.cbm
Subject: Re: Questions about 128 Reliability (Considering upgrade from C64)
Message-ID: <10342@s.ms.uky.edu>
Date: 7 Oct 88 15:04:29 GMT
References: <205.234963B0@isishq.FIDONET.ORG> <39729@yale-celray.yale.UUCP>
Reply-To: simon@ms.uky.edu (Simon Gales)
Organization: U of Kentucky, Mathematical Sciences
Lines: 31

In article <39729@yale-celray.yale.UUCP> sekora-jay@CS.YALE.EDU (Jay Sekora) writes:
>In article <205.234963B0@isishq.FIDONET.ORG> Geoffrey.Welsh@isishq.FIDONET.ORG (Geoffrey Welsh) writes:
>> <deleted>
>> 
>>   While it is correct that only one CPU is operating at any given 
>>instant, it should be noted that CP/M I/O is done by the Z80 switching 
>>the 8502 in (i.e. I/O code is performed by the 8502 at the Z80's request).
>> 
>>   Geoff ( watmath!isishq!izot )

>My understanding is that this was true of the CP/M add-on card for the C64,
>but that on the 128 the Z80 does all it's own i/o and doesn't have to rely
>on the 8502 for anything.  
> <Deleted>

The Z80 in the 128 DOES use the 8502 for its i/o, although I am not
quite sure why.  The Z80 seems to be able to access all of hardware (or
can it?), is using the 8502 faster?  Maybe they did it to keep the
cp/m kernal (?) smaller...?   The Z80 is in control on power up, it is
the one that decides whether to go into cp/m or cbm mode.
							Simon.

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<---   Simon Gales@University of Ky                 254-9387/257-3597   --->
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<---   Simon Gales@University of Ky                 254-9387/257-3597   --->
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