[Coco] Extended Basic Upgrade Options

[Dave Philipsen]

Yeah, might also be that at the time the CoCo was designed the industry 
had not yet settled on a standard (JEDEC) for 64k-bit ROM/EPROM chips.  
Before the 2764 the other chips were all 24-pin chips (2708, 2716, 
2732).  As I recall, a lot of stuff was in flux then.  Seems like there 
were at least two different types of 2764s also because of programming 
voltage differences.  In fact, the 68764 required a 25v programming 
voltage and the newer chips were being programmed with 21v and 12.5v.

Dave Philipsen


On 4/7/2015 12:31 PM, Al Hartman wrote:
> One would guess Tandy did this because that kind of masked ROM was 
> cheaper, and it made it less likely the average user would pirate a 
> ROM rather than taking their Coco to a Computer Center to purchase a 
> real one.
>
>
> -[ Al ]-
>
>
> On Tue, Apr 07, 2015 at 01:21 PM, Dave Philipsen wrote:
>
>> Yes, but that's only a 32k-bit EPROM which means it's 4K-byte and not 
>> large enough for the BASIC ROM in a CoCo.
>>
>> The problem is that whoever designed the CoCo decided to use the 
>> 68764 pinout for the ROMs which is different from the defacto 
>> industry standard 2764.  Apparently Commodore used this ROM in the 
>> C64 as well.
>>
>> Dave Philipsen
>
>