homemade computer for fun and experience...

From: Richard Erlacher <edick_at_idcomm.com>
Date: Fri Apr 9 01:39:35 1999

A reasonable example of how to do these things would be available in the IBM
PC Technical Reference, since their display boards used the 6845. The
scheme is based on the notion of SHARED memory. The processor writes to the
video memory, or to the character memory, and the 6845, once initilized,
generates the cursor, and scans through memory at the proper rate to effect
display of the content. Unfortunately, Motorola unfortunately didn't
include a delay stage to allow for translation of ASCII data to video, so an
external latch has to be used to delay sync and blanking by a character
clock period, which means you might have to accomodate that in your sync
timing as well. it means there will be a 1-character period offset between
blanking and character video while the graphics will be "right on."


-----Original Message-----
From: jpero_at_cgocable.net <jpero_at_cgocable.net>
To: Discussion re-collecting of classic computers
<classiccmp_at_u.washington.edu>
Date: Thursday, April 08, 1999 11:28 PM
Subject: Re: homemade computer for fun and experience...


>On my homebuilt computer quest.......
>
>There's two groups:
>Built in video and serial i/o to terminal attached concepts.
>
>Can you explain the process to "init" and operate video chip based
>on 6845 chip with own ram ? Possible to use SRAM with it?
>Is there CPU specific limitations?
>
>I have many of them and certainly get put in use on computer.
>
>And alteratives:
>
>How one place characters on terminal, give examples of terminal
>coding as sent from computer to terminal?
>
>-outputting characters to screen?
>-resetting cursor to different places?
>
>Which CPU is very friendly for creating basic codings to put into
>ROM and assembling? Z80? or suitable CPU?
>
>Thanks!
>
>Wizard
Received on Fri Apr 09 1999 - 01:39:35 BST

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