Subject: Re: Memory Map for IIe (64K & 128K versions?) From: Rubywand Date: Sat, Oct 24, 1998 16‚1 Á Message-id: <36325C65.4C7D016D@swbell.net> David Empson writes ... .... > > > > KEYBOARD = $C000 ;keyboard data (latched) (RD-only) > > Bit 7 is set to indicate a keypress is waiting, with the ASCII code in > bits 6-0. And, Bit 7= 1 means only that "a character key-press has been recognized by the KB (keyboard) since the last time Bit 7 was cleared to 0 via an access to $C010". That is, Bit 7 of $C000 is a flag which only the KB can set and only the System can clear. Also, the status of Bit 7 has no effect upon Bits 0-6 of $C000. > > > CLR80COL = $C000 ;use 80-column memory mapping (WR-only) > > SET80COL = $C001 .... > > Note that all the $C000-$C00F mode switches are write-only. > Yes; that info should be included to avoid confusion. > > STROBE = $C010 ;strobe (unlatch) keyboard data > > This can be read or written for the unlatch function. > > If read, it also provides an "any key down" flag in bit 7, with the > keycode in the remaining bits. (These features only apply to the IIe > and later machines.) That's a nice feature. It's too bad it was not included in the II and II+. .... > > CLRC8ROM = $CFFF ;switch out slot C8 ROM > > Reading any location from $Cn00-$CnFF (where n is the slot) will enable > the $C800-$CFFF area for that card, if the card supports this feature. > Reading $CFFF disables this area for all cards. > > The $C800 space is a further 2K area normally used for firmware > expansion by cards that can't fit their code in 256 bytes (most of > them). Some cards have RAM and/or I/O in this area, and some use > internal bank switching to get even more space. > Yes; we did this with our II+ Monitor expansion placed on a card in Slot 7. It gave us 4kB of space to add bunches of neat features. .... > > $8000 --- (Approximately)--- This is the typical 'safe' upper limit > > for the BASIC program area (i.e. for Program + variables) when > > DOS or ProDOS are also present. DOS 3.3 usually allows going a > > bit higher. > > The upper limit is actually $9600 for both operating systems, unless you > need to open files under ProDOS. ProDOS automatically manages the HIMEM > limit as required (moving variables out of the way), so the usable upper > limit will vary depending on your file access requirements. > > With DOS 3.3 you have to explicitly set the maximum number of open > files, and memory availability is adjusted accordingly. DOS 3.3 MAXFILES does have a built-in default, though-- 3 files. .... Thanks for the corrections and additional info! Rubywand