David Schmidt wrote:

>   I'm looking for a darlington driver chip like the
> ULN2003 but with 8 internal driver channels instead of
> 7.  Anyone have a part number for such a part?

Yes, there is such a beast (8 or 9 channel peripheral driver).
Unfortunately, I'm not near my IC master right now so cannot look it up.
ULN28XX seems to ring a bell though...

> BTW, why does SIP pullup resistor networks come with 9 or 5
> resistors instead of 4 or 8?

Because almost all packages come with an even number of pins. The same
10 pin SIP can hold 5 isolated resistors, 9 single common bus (pull-up
or down) resistors, or 8 termination network (pull-up and down)
resistors.

You CAN get 9 pin pull-up or down SIP resistor packs, but they are hard
to get, and consequently expensive. I usually lay out a board with a
larger SIP size, with the end resistor(s) unused. That way the board can
take a larger SIP when a smaller one may be temporarily unavailable on
short notice.

> Why is the ULN2003 7 channels instead of 8?  With 4/8/16/32/64 bit computers
 you'd think
> they would make parts along those numbers instead.

Well, the ULN200X series was never designed to drive data or address
busses, so there is no relation seen. The series are PERIPHERAL drivers
(relays, lamps, high voltage loads, etc). Thats the reason for the catch
diode connection, for inductive loads like relay or printer hammer
coils. The 18 PDIP package was introduced many years after the ULN200X
series was introduced (8, 14, 16, 24, 26, 28, & 40 PDIPs were common). A
16 PDIP can accomodate 7 drivers, a GND, and a catch diode common.

Today, we are spoiled with the selection of package styles, mounting
options, and densities available. 15 years ago it was a PDIP, CDIP, and
TO-10 type can package world!

--
Regards, Dana Frank Raymond