On Tue, May 17, 2022 at 12:35 AM ben via cctalk
wrote:
> Did DEC not use a few Non TTL chips to reduce I/O loading on the bufferd
> lines?
>
DEC used non-TTL buffer chips for bus interface (Omnibus, Unibus, Qbus, and
external buses like Massbus). Most of the other SSI/MSI logic chips are TTL
or
On 2022-05-16 1:50 p.m., Eric Smith via cctalk wrote:
On 2022-May-15, at 3:53 PM, Eric Smith wrote:
I specifically said 74x74. Early TTL flipflops were very crude by
comparison.
On Mon, May 16, 2022 at 11:28 AM Brent Hilpert via cctalk <
cctalk@classiccmp.org> wrote:
pre-TTL != early TTL
Murphy
Subject: Re: Replacement for a DEC 7474 Chip
On May 16, 2022, at 4:59 PM, Rob Jarratt via cctalk mailto:cctalk@classiccmp.org> > wrote:
I have several 7474s, including one marked DEC 7474. Sadly, I fear that
shipping from the US is likely to be prohibitive.
I have o
> On May 16, 2022, at 4:59 PM, Rob Jarratt via cctalk
> wrote:
>
>> I have several 7474s, including one marked DEC 7474. Sadly, I fear that
>> shipping from the US is likely to be prohibitive.
>
> I have ordered some 7474s. However I am getting a bit lost in the discussion
> now. From a
> -Original Message-
> From: cctalk On Behalf Of Rick Murphy via
> cctalk
> Sent: 16 May 2022 17:28
> To: cctalk@classiccmp.org
> Subject: Re: Replacement for a DEC 7474 Chip
>
> On 5/15/2022 4:16 AM, Eric Smith via cctalk wrote:
> > On Sat, May 14, 202
On 2022-May-15, at 3:53 PM, Eric Smith wrote:
> I specifically said 74x74. Early TTL flipflops were very crude by
comparison.
On Mon, May 16, 2022 at 11:28 AM Brent Hilpert via cctalk <
cctalk@classiccmp.org> wrote:
> pre-TTL != early TTL
>
No, but 7470, 7472, 7473, and 74948 were _very_ early
On 2022-May-15, at 3:53 PM, Eric Smith wrote:
> On Sun, May 15, 2022, 13:03 Brent Hilpert via cctalk
> wrote:
> On 2022-May-15, at 1:16 AM, Eric Smith via cctalk wrote:
> > On Sat, May 14, 2022, 16:09 ben via cctalk wrote:
> >> On 2022-05-14 11:50 a.m., Nigel Johnson Ham via cctalk wrote:
> >>>
On 5/15/2022 4:16 AM, Eric Smith via cctalk wrote:
On Sat, May 14, 2022, 16:09 ben via cctalk wrote:
On 2022-05-14 11:50 a.m., Nigel Johnson Ham via cctalk wrote:
AFAIR LS can only drive one unit TTL load.
paul
LS is 4 TTL, 4 ma low.
Was there a trick of forcing the output of D flip
I specifically said 74x74. Early TTL flipflops were very crude by
comparison.
On Sun, May 15, 2022, 13:03 Brent Hilpert via cctalk
wrote:
> On 2022-May-15, at 1:16 AM, Eric Smith via cctalk wrote:
> > On Sat, May 14, 2022, 16:09 ben via cctalk
> wrote:
> >> On 2022-05-14 11:50 a.m., Nigel
> On May 15, 2022, at 2:51 PM, Chris Quayle via cctech
> wrote:
>
> ...
> Original 74 series TTL can still be found, Ebay often, new old stock
> and other surplus vendors.
>
> Would need to take care replacing with later ttl series, as the gate
> delay, switching times and fanout probably
On 2022-May-15, at 1:16 AM, Eric Smith via cctalk wrote:
> On Sat, May 14, 2022, 16:09 ben via cctalk wrote:
>> On 2022-05-14 11:50 a.m., Nigel Johnson Ham via cctalk wrote:
>>> AFAIR LS can only drive one unit TTL load.
paul
>> LS is 4 TTL, 4 ma low.
>> Was there a trick of forcing the
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Today's Topics:
1. Replacement for a DEC 7474
What ever you do, don't use a Fairchild part. When I worked for Intel in
the 80's, we finally band using Fairchild for any latching device. They
failed on pullup current, even when the parts were sent back and they
claimed they were good. We just gave up on them, we couldn't hold
production
nal Message-
> From: cctalk On Behalf Of Chuck Guzis via
> cctalk
> Sent: 15 May 2022 16:12
> To: cctalk@classiccmp.org
> Subject: Re: Replacement for a DEC 7474 Chip
>
> On 5/15/22 01:16, Eric Smith via cctalk wrote:
>
> > I don't think that worked on any TTL (or C
On 5/15/22 01:16, Eric Smith via cctalk wrote:
> I don't think that worked on any TTL (or CMOS) 74x74 flip flops, except
> maybe by accident if you shorted the output enough to draw Vcc down (or
> ground up) enough to disrupt the FF, and then you have other problems.
Checking my old Moto
On 5/14/22 23:04, ben via cctalk wrote:
> Faster is not better, bigger is bett... ops wrong topic.
>
> 74H while slower, and 74S tend to have reliable delay times looking at
> gates with min to max delays < 3 ns. This helped devices to track
> the same speed across a system.
> A 74ABT00 is 1 to
On Sat, May 14, 2022, 16:09 ben via cctalk wrote:
> On 2022-05-14 11:50 a.m., Nigel Johnson Ham via cctalk wrote:
> > AFAIR LS can only drive one unit TTL load.
> >> paul
> LS is 4 TTL, 4 ma low.
> Was there a trick of forcing the output of D flip flip
> to clear it? I was wondering if this
amaged,
> and I ordered a Fairchild 74LS08! I will ask them to change it for a
> Motorola part they also have.
>
> > -Original Message-
> > From: cctalk On Behalf Of dwight via
> cctalk
> > Sent: 14 May 2022 23:36
> > To: Paul Koning via cctalk
> &
cctalk On Behalf Of dwight via
cctalk
> Sent: 14 May 2022 23:36
> To: Paul Koning via cctalk
> Subject: Re: Replacement for a DEC 7474 Chip
>
> What ever you do, don't use a Fairchild part. When I worked for Intel in
the
> 80's, we finally band using Fairchild for any latching device.
I'll have to check when I get back from Norway but I believe I replaced thirty
or so flip flops with 74ls74 chips with no problems. This was on my pdp8l and
granted Dec used a lot of 4 and 8 input nand gates to drive loads
On May 15, 2022 12:08:55 AM GMT+02:00, ben via cctalk
wrote:
>On
On 2022-05-14 10:53 p.m., Chuck Guzis via cctalk wrote:
On 5/14/22 15:35, dwight via cctalk wrote:
You are stuck with using an original 7474 family assuming this is driving other
early TTL. 74LS74, and others simply don't have the drive capability to work.
I know LS has less fanout, but is
On 5/14/22 15:35, dwight via cctalk wrote:
>>> You are stuck with using an original 7474 family assuming this is driving
>>> other early TTL. 74LS74, and others simply don't have the drive capability
>>> to work.
>> I know LS has less fanout, but is it not able to drive plain 74xx at all?
>>
: Saturday, May 14, 2022 10:50 AM
To: Paul Koning via cctalk
Subject: Re: Replacement for a DEC 7474 Chip
AFAIR LS can only drive one unit TTL load.
I may have some 7474, even of that vintage, if you cannot find any
anywhere else.
cheers,
Nigel
Nigel Johnson, MSc., MIEEE, MCSE VE3ID/G4AJQ/VA3MCU
On 2022-05-14 11:50 a.m., Nigel Johnson Ham via cctalk wrote:
AFAIR LS can only drive one unit TTL load.
paul
LS is 4 TTL, 4 ma low.
Was there a trick of forcing the output of D flip flip
to clear it? I was wondering if this is what kills all
the 7474's?
Ben.
AFAIR LS can only drive one unit TTL load.
I may have some 7474, even of that vintage, if you cannot find any
anywhere else.
cheers,
Nigel
Nigel Johnson, MSc., MIEEE, MCSE VE3ID/G4AJQ/VA3MCU
Amateur Radio, the origin of the open-source concept!
Skype: TILBURY2591
On 2022-05-14 13:48,
> On May 14, 2022, at 1:41 PM, John Robertson via cctalk
> wrote:
>
> On 2022/05/14 10:11 a.m., Rob Jarratt via cctalk wrote:
>> Hello,
>>
>> I have found a bad DEC 7474 chip on my M7133 board. Clearly it is a
>> 7474 D flip flop. The problem is I don't know which modern series
>> would be
On 2022/05/14 10:11 a.m., Rob Jarratt via cctalk wrote:
Hello,
I have found a bad DEC 7474 chip on my M7133 board. Clearly it is a
7474 D flip flop. The problem is I don't know which modern series
would be the best one to replace it with. I am sure I have seen a list
somewhere of modern
Hello,
I have found a bad DEC 7474 chip on my M7133 board. Clearly it is a
7474 D flip flop. The problem is I don't know which modern series
would be the best one to replace it with. I am sure I have seen a list
somewhere of modern equivalents for some DEC chip numbers, but I can't
remember
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