patth@dasys1.UUCP (Patt Haring) (07/30/87)
Apple //e Hardware Technical Note #8 - Known Anomalies of
the New //e ROMs
Written: 6/84
Verified by: Cameron Birse 2/86
------------------------------------------------------------
This technical notes describes three current problems, and
some possible workarounds for them.
------------------------------------------------------------
The following three anomalies are known to occur when the
new //e ROMs are present:
1) If the new //e ROMs are used with interrupts active when
a combination of certain printer cards (Versacard, Uniprint,
Graphitti, PSIO cards) along with the mousecard are present
in the system, the system will hang when printing is
attempted. This is possibly caused by a spurious interrupt
occurring from the mousecard. The problem can be avoided by
disabling interrupts while printing to a printer card. For
more information on the general architecture of the //e and
how the ROMs handle them see: "Interrupts on the Apple //e"
by Ernie Beernink, 20-May-84.
2) There may be some problems when using the ROMs with
communications packages. This is due to the way that the 80
column firmware switches into 40 column mode. By sending a
control-Q through COUT the firmware to switches into 40
column mode. A simple solution to this would be to send an
ESC-CTL-D sequence which disables the control functions.
This will remain in effect until either the 80 column card
is re-initialized by PR#3 or an ESC-CTL-E is sent through
COUT. Another solution would be to simply not allow
control-Q's to get through to COUT by filtering them before
they get there.
3) Many developers using double high resolution
(dbl-hi-res) graphics may wish to use 40 column text
displays so that the text can be read on a television set.
There are a couple of possibilities:
A.) You can define your own dbl-hi-res character set with
any size characters you desire and then plot them on the
dbl-hi-res screen.
B.) You can print text to the Apple //e text screen and
toggle the screen on to display it.
NOTE: There is no way to display 4 lines of 40 column text
at the bottom of the dbl-hi-res screen in mixed mode since
the 80 column hardware must be active while dbl-hi-res is
being displayed.
#To use the second method, however, does require some
special considerations.
The Apple //e scroll routines continues to use the window
parameters when scrolling, but uses the 80COL softswitch to
determine if it should scroll the 80 or 40 column screen.
Since the firmware has initialized a 40-column window, the
scroll routines will move only the first 40 columns. But,
the 80COL flag has been turned on for dbl-hi-res!
Therefore,
the scrolling routine takes every even column from auxiliary
memory and every odd column from main memory. As a result,
only the first 40 columns get scrolled, 20 columns from
auxiliary memory and 20 columns from main memory.
One possible solution to the problem is to write your own
scroll routines. Another might be to write to the screen so
that scrolling will not occur. But there is yet another
solution. Turn on the full 80 column mode with a "PR#3" or
the equivalent. Now print your text to COUT in the normal
manner being careful not to exceed 40 characters per line.
The 80 column firmware will scroll everything properly.
When you are ready to display text, send a CONTROL-Q through
COUT to switch to 40 columns. When you are ready to return
to dbl-hi-res mode, send a CONTROL-R to COUT.
When switching modes, a momentary "glitch" may occur. If
you send the CONTROL-Q to COUT while still in graphics mode
the screen will go to regular "single" hi-res mode before
finally going to text mode. If you switch to text mode
first, the text will be in 80 column mode (with 40 columns
displayed on the left half of the screen) before ultimately
going to 40 column mode. The same potential glitch may
occur going back to dbl-hi-res. The "glitch" will be only
momentary and may not present any problem for your
application.
--
Patt Haring UUCP: ..cmcl2!phri!dasys1!patth
Big Electric Cat Compu$erve: 76566,2510
New York, NY, USA MCI Mail: 306-1255; GEnie: PATTH