Path: utzoo!utgpu!watmath!isishq!f171.n221.z1.FIDONET.ORG!izot
From: izot@f171.n221.z1.FIDONET.ORG (Geoffrey Welsh)
Newsgroups: comp.sys.cbm
Subject: Re: C128,C128D, and C128C??? Questions
Message-ID: <1856.2423BC06@isishq.FIDONET.ORG>
Date: 14 Mar 89 14:09:01 GMT
Sender: ufgate@isishq.FIDONET.ORG (newsout1.25)
Organization: FidoNet node 1:221/171 - Izot's Swamp, Kitchener ON
Lines: 66


 > From: fred@cbmvax.UUCP (Fred Bowen)
 > Message-ID: <6222@cbmvax.UUCP>
 
 >>I have plenty of "why didn't you do that
 >>in the first place" questions for the designers of the C128...
 >
 >I have plenty of "why didn't we do that" answers, BTW...
 
   Gee, this could be interesting.
 
(1) Why didn't the C128 include 64K video RAM from the beginning? Considering 
that the VDC was designed to handle 2 4416s or 8 4164s (but has also proved 
workable with 2 4464s), it seemed the logical thing to do...
 
(2) Given that the 128's MMU could handle FOUR 64K banks of memory, why was 
that capability not used? 41256s were a commodity chip at the time and I find 
it difficult to believe that Commodore was afraid that the C64 wouldn't clear 
out its inventories of 4164s...
 
(3) I find it incredibly amusing that the Z80 runs at an effective 2 MHz even 
though the VIC-II is enabled because it runs 4 MHz, 2 cycles on and 2 off. 
Would producing a 4 MHz 8502 have ben so expensive that a similar scheme could 
not have been used to allow 128 mode to support 2 MHz, even in 40-column mode? 
Better yet, why does there not seem to be a way to shut doen the VIC-II chip 
in CP/M mode and run the Z80 flat out at 4 MHz (Jeez, it would have been nice 
to do that in C128 mode as well)...
 
 > Geoffrey's discription (deleted) was good, but the info above is
 > incorrect.  Interlaced screen resolutions up to 640x600 (that's six
 > full Doodle screens complete with color) are possible.
 
   That's what I thought from reading the VDC specs, but I wasn't able to 
achieve it. Since I am not a video specialist (that is probably the area where 
I lack experience most), I figured at first that it was me. However, I have 
been told by several people (including a fellow named Jeff Solomon, who claims 
to be a "Commodore rep") that there is a bug in the VDC that prevents bitmap 
and interlace modes from being enabled at the same time.
 
 > Examples of
 > C128D interlaced and overscan screens have been published in TC128,
 > and are available on QLink, GEnie, and probably elsewhere.
 
   Well, it's been years since I realized that QLink and GEnie, while good 
fun, simply cost way too damned much (same for Compu$erve). I never subscribed 
to TC128 (more's the pity... I really enjoyed the Transactor).
 
   Thanks for the info, Fred.
 
============================================================================
Usenet:    watmath!isishq!izot                       | 66 Mooregate Crescent
Internet:  Geoffrey.Welsh@f171.n221.z1.fidonet.org   | Suite 602
FidoNet:   Geoffrey Welsh on 1:221/171               | Kitchener, Ontario
PunterNet: 7/GEOFFREY WELSH                          | N2M 5E6 CANADA
BBS:       (519) 742-8939 24h/7d 9600 USRobotics HST | (519) 741-9553
============================================================================
|  "I don't need a disclaimer. No one pays any attention to what I say."   |
============================================================================
 
 


--  
 Geoffrey Welsh - via FidoNet node 1:221/162
     UUCP: ...!watmath!isishq!171!izot
 Internet: izot@f171.n221.z1.FIDONET.ORG