Re: SwyftCard

["Paul R. Santa-Maria" <paulrsm@buckeye-express.com>]

"Michael J. Mahon" wrote:
> David Wilson wrote:
> > Interesting card. I can see what the EPROM and PAL chips are for but
> > why does it need an LM311 voltage comparator?
> Reset timer?

Exactly.  Below is an excerpt from the manual.
I have sent the manual, which also contains
a circuit diagram, to the csa2 gmail account.

--
Paul R. Santa-Maria
Temperance, Michigan USA


SwyftCard Hardware Theory of Operation

The SwyftCard is a plug-in card for the 
Apple IIe that operates in Slot 3.  The 
card contains three integrated circuits 
which provide a power-on reset circuit, 
storage for the SwyftCard program, and 
control signals for the card.  The card 
operates by asserting the Apple IIe bus 
signal INH' which disables the built-in 
ROM and enables the SwyftCard ROM.  This 
permits the SwyftCard program to take 
over the system at power-on and run the 
SwyftCard program.  (Please refer to the
schematic.)

The LM311 voltage comparator is 
connected to provide the power-on reset 
function.  When the Apple IIe is first 
turned on, the power-on reset circuit 
resets the PaL, turning on the SwyftCard 
and disabling the Apple IIe internal 
ROM.  The power-on reset circuit must be 
provided because the existing Apple IIe 
reset function is used by many Apple IIe 
programs for a "warm start": if Apple 
IIe reset always started the SwyftCard, 
other programs could not use the "warm 
start."

The 27128 PROM is used to store the 
SwyftCard program.  The PROM contains 
16384 bytes which are mapped into the 
address space $D000-$FFFF.  Since the 
address space is only 12 Kbytes, there 
are two 4 Kbyte sections of the PROM 
mapped into the address space 
$D000-$DFFF.

The card is controlled by the PAL.  When 
the SwyftCard is active, the PAL asserts 
the INH' signal, enables the PROM, and 
bank switches the $D000-$DFFF address 
space.  The card is controlled by two 
soft switches.  The soft switches are 
controlled by accessing the following 
memory locations with either a read or a 
write operation.

  $C0B0 - SwyftCard active, Bank 1
  $C0B1 - SwyftCard inactive, Bank 1
  $C0B2 - SwyftCard active, Bank 2

When the power-on reset circuit asserts 
the RES signal on pin 3 of the PAL, the 
SwyftCard is made active in bank 1.  
Accessing location $C0B1 deactivates the 
SwyftCard for normal Apple IIe 
operation.

The INH' line is driven by a tri-state 
driver, so if another card in the Apple 
IIe asserts the INH' signal there will 
not be a bus contention.  However, there 
will be a bus contention on the data bus 
if another card attempts to control the 
bus while the SwyftCard is active.