[Coco] How to tell if running on a Coco3 versus 1 or 2?

[Robert Gault]

One thing you might try is to see if the CoCo3 hardware is present. Only the CoCo3 has a control at $FF90 which can select how much internal ROM is present. You can set $FF90 for 32K internal ROM and if the ROM code changes at $C000, you have a CoCo3. Read the CoCo3 service manual.

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  On Sat, Jul 23, 2022 at 7:31 AM, Don Barber via Coco<coco at maltedmedia.com> wrote:   Hi folks, writing some assembly and have come across a need to determine 
if the code is running on a coco3 versus a 1 or 2. Right now its mostly 
for display output purposes (checking HRWIDTH to determine which screen 
size is in use doesn't work on coco1/2s that don't have alternate screen 
sizes so need to default to 32-column behavior on the older machines).

My first instinct is to go through the Super basic unravelled book and 
find something different about the coco3 code like the destination 
location for a ram hook or interrupt vector and check for that, or maybe 
check the startup message for version 2.x, or something similar. But it 
occurs to me that someone else has probably solved this problem already. 
Any advice?

Don


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