Re: Success - first hires graphics ;)

----- Original Message ----- 
From: "vossi" <vossi@ceffy.de>
To: <cbm-hackers@musoftware.de>
Sent: Friday, September 08, 2017 1:59 AM
Subject: RE: Success - first hires graphics ;)


> Hi Ruud,
> 
> I know that VPP must be +5V for read, but the question is:
> 
> Are the outputs in Hi-Z if VPP is at lo-level / then VPP is a an additional
> CS-pin ???
> I think it's possible that this is eprom-type-dependent...
> 
> In the 8032-schematic the pin21 (VPP) is with all clear-inputs together at
> the init-line and this is tied with a 1k resistor to +5V.
> -> So you can use a 2716 instead a 2316/2332-char-rom.

I don't think so. This issue has come up when replacing the 8032 ROMs in a SuperPET where pin 21 (/NOROM) is used to disable the PET ROMs in SP mode; from a vcfed discussion:

"Okay....so from what I understand, with an original Commodore/MOS produced EDIT ROM (UD7) in a SuperPET, a low (ground?) on PIN 21 is a NOROM signal, thereby disabling that ROM. When pin 21 is low, the ROM refuses any READ requests from the CPU. Correct?

However, the problem with using an EPROM like the 2716 or 2732 as an EDIT ROM is that a "low" signal on pin 21 does NOT disable these types of chips. The EPROM merrily continues to accept READ requests and therefore conflicts with the SuperPET's daughterboard ROMS when 6809 CPU mode is enabled. Correct?

So the solution is to rig something that will disable UD7 some other way, every time the NOROM line is set to low. Correct?"



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