1 Oct
2011
1 Oct
'11
10:21 a.m.
I was still thinking about reading PAL/HAL/bipolar ROM
in 0.300" wide
DIP sockets. I'm not aware of a PAL with center-fed power, are you?
All the PALs/HALs/GALs I'ev used (in DIL pacakges)_ have corner power
pins. However I was looking at a more general solution because I have
some very odd machines with very odd programamble devices.
As far as power for EPROMs and the like, that could be handled pretty
easily, as for most devices, it's Vcc that moves around a bit. Some
_Most_ EPROMs have corner power and ground pins. There are exceptions
(and even nore exceptions when you look at mask ROMs).
I have an old Logical Devices universal programmer somewhere. It's pretty
useless because I've never managed to finf the PC interface card or
software fro it. Anyway, it has a 40 pin ZIF socket and 5 pin driver
boards, each driving 8 og the pins (with one exception, see below). From
what I rememebr, there are 3 or 4 programable PSUs inside (set by DACs),
the pin driver can connect a pin to any one of them or ground. Said pin
drivers are stuffed with ULNxxxx buffer ICs, not suprisingly... Oh yes,
they scratched hte numbers off the ICs, but that puzzled me for at least
an hour.
Anyway, the exception. Pin 20 -- the bottom left corner -- of the ZIF
socket is directly connected to ground. Apparently getting a solid ground
is harder than it looks, and pretty important. And I guess all the
devices this programmer could support had ground in that corner.
-tony