2 Jun
2006
2 Jun
'06
9:52 a.m.
On 6/2/2006 at 7:03 AM dwight elvey wrote:
I have 9xx DTL in my Nicolet 1080 and it runs on 5
volts, not 6 volts.
DTL can, for the most part be replaced by TTL with the same pinouts.
That is except one case. I don't recall the number but there is a DTL
gate that can be expanded externally with more diodes to create
a wider input.
Early 7400-series TTL had the 7450 and 7453 AND-OR-INVERT gates that could
be explanded with another 4 inputs via the 7460 dual 4-input expander. I'd
hate to own equipment now that used some of those that required
replacement--they must be very difficult to find.
The bigger problems in replacing DTL with TTL (other than the obvious
impedance mismatch issues) is that DTL could use a relatively wide range of
supply voltages (up to 8 volts) and outputs could be wire-OR-ed with
relative impunity (i.e. you didn't have to consult the databook to see if
you could do it). And yes, expandable gates were more common. In addition
to flat pack and DIP, DTL could also be furnished in TO-100 cans; which led
to the interesting situation that you could have two packages with the same
base part number but with a different number of active pins (e.g. MC833P
vs. MC833G). For Moto, DTL devices were, by and large, the 830/930- 960
families, with some late parts having numbers in the 1800-1900 range.
There was an old DTL 200/250 series, but I've never seen equipment that
used it. There was also a "radiation hardened" line of DTL, the MCE930
series that featured nichrome resistors and dielectric isolation of circuit
elements from the substrate.
RTL also featured expandable gates, but with an interesting twist the
expanders (basically open-collector gates) could be used on just about any
other RTL device--you didn't need the base device to be one of the
"expandable" versions Again, wired-OR operation was very common.
Where I'd be stuck is finding replacements for HTL--15 volt Vcc and the
switching threshold somewhere around 7 volts.
Cheers,
Chuck