Re: No-Slot Clock in Apple ][+?

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

In article <44cik1$h8m@news.tamu.edu>,
John Donald Baker <jdb8042@tam2000.tamu.edu> wrote:
> 
> Has anyone successfully installed the No-Slot Clock
> (aka Dallas Semiconductor DS1216E) in an Apple ][+?
> Can it be done at all?

There is the obvious problem of the chip size and supply of power to
the SmartWatch (solvable with a single wire mod).

The second problem is that the ][ and ][+ ROMs are not quite
compatible with EPROMs.  In particular, the Chip Select signal (pin 18
on a 24 pin chip, pin 20 on a 28 pin chip) is active high in the ][
and ][+, while it is active low for an EPROM.

The DS1216E expects an active low signal on this pin, and conditions
it to prevent conflicts with the ROM when the time is being read.

Another problem is that the chip select signal on pin 18 is
permanently active, except while the INHIBIT signal from the slots is
in use.  The ROMs are actually selected using pins 20 and 21 (active
low chip selects).

This problem is not solvable without some add-on hardware.  You would
have to re-route the select signal from pin 20 of the ROM socket (22 on
the DS1216E) to pin 20 on the underside of the DS1216E, then invert the
signal coming out of pin 20 before it went into the ROM, or re-route
it back to pin 20 of the ROM, and leave pin 18 of the ROM going
through to the Inhibit signal (not a good idea - Inhibit should
probably be gated into the enable signal going into the SmartWatch).


A better solution would be to put the DS1216E under a 28-pin EPROM in
a card in one of the slots, e.g. that of a SCSI card.  Unfortunately,
most ][/][+ cards only have 24-pin EPROMs, but this is solvable with a
wire mod to get power to the SmartWatch.
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand