Re: Apple II plus motherboard character generator

[dempson@actrix.gen.nz (David Empson)]

Vince Briel <vbriel@yahoo.com> wrote:

> I have my Apple II plus to the point it beeps, displays "Apple ][", but
> text is block graphics instead of alpha-numberic characters.

It sounds like the computer is stuck displaying lo-res graphics mode.
This mode uses the same memory area as the text screen, with two blocks
corresponding to each text character (splitting the characters in half
vertically, for a total of 40 columns and 48 rows in full screen mode).

There four related soft-switches which control the video display mode,
each of which has two states.  They are:

GR or TEXT
FULLSCREEN or SPLITSCREEN
PAGE1 or PAGE2
LORES or HIRES

If TEXT mode is enabled, the SPLITSCREEN and HIRES soft switches are
ignored.  If GR mode is enabled, then FULLSCREEN/SPLITSCREEN toggles the
bottom four lines of the screen between text and graphics mode, and
LORES/HIRES selects between lo-res graphics (described above) and hi-res
graphics (pixel-based).

The PAGE1/PAGE2 switch works in all modes - it selects which of the two
buffer areas are displayed on the screen.

It sounds like your GR/TEXT softswitch is stuck in GR mode.  The reset
code switches it to TEXT mode, and this is obviously being ignored.

This could be as simple as a dry joint, corroded track or short on the
relevant signal line.

I don't have a sufficiently detailed II+ reference handy, so I can't say
precisely where on the motherboard the problem might be.

-- 
David Empson
dempson@actrix.gen.nz