[Coco] Coco 2b problem: reboots when accessing the disk

[Darren A]

On Mon, Feb 25, 2013 at 10:15 PM, Luis Antoniosi (CoCoDemus) wrote:
> Hi,
>
> I have this coco2b and when doing a DIR  with a FD500 it reboots with
> garbled screen. If the drive is not connected it returns I/O Error.
>

That sounds like either the CPU's HALT or NMI lines are blown.  With
the floppy controller connected, you can enter this one-liner to test
HALT:

POKE &HFF48,3:POKE &HFF40,128

If HALT is working correctly, the computer should freeze for about 8
seconds and then the OK prompt will return.

To test both HALT and NMI together, you can use the following program:

10 POKE &H600,&H7C
20 POKE &H601,4
30 POKE &H602,0
40 POKE &H603,&H3B
50 POKE &H109,&H7E
60 POKE &H10A,6
70 POKE &H10B,0
80 POKE &HFF48,0
90 POKE &HFF40,&HA0
100 GOTO 80

When you run this program the character in the top-left corner of the
screen (standard 32 column mode) should increment once every 1.5
seconds.  Again, a floppy controller is required for this test.

Darren