15 Oct
2012
15 Oct
'12
6:17 p.m.
On 10/15/2012 02:31 PM, Tom Uban wrote:
On 10/14/12 8:40 PM, Eric Smith wrote:
I understand the specs but, there are boards out there using standard
TTL in the form of LS244,
LS241, LS245 and I've interfaced to Q-bus using those. Whats the issue?
Hint if your building a multibackplane system then it _may_ be an issue.
The H11 boards (IO, memory and storage) use mostly regular parts. Same
for a lot of other non-DEC
vendors.
The key thing here is we are worrying only one board and even is the
leakage is a little high the system
will run as all the other boards are hopefully conforming.
The biggest issue is getting all of it on a quad or even a dual board.
With current modern Flash
and SD and CF devices the actual storage medium is a non issue.
Has any one considered this scsi to Flash/SD/CF memory emulating a
disk. This may be of interest
for those with SCSI and those getting scarce.
Me I planed ahead and kept all the small drives that people didn't want
but still ran from older
MFM and IDE to SCSI. That and old boards even if flagged dead.. they
can be fixed or used for parts.
Allison
I wrote:
With a discrete design, the propagation delay is likely to go up. Is there
a maximum prop delay criteria?
meeting the maximum leakage current spec is quite
difficult.
Dave McGuire wrote:
Why? (if you want to go into it)
The
requirements are basically:
Vol 0.7V max into 70 mA load
Vil max 1.3V
Vih min 1.7V
minimum 5 ns rise and fall times (10% to 90%)
80uA max leakage at 3.8V, 10uA max at 0V (with Vcc from 0.0V to 5.25V)
10pF max capacitance
My attempts to design anything that meets this failed on either the leakage current,
capacitive
loading, or both. However, someone who is more skilled with analog design could probably
come up
with something satisfactory.
Even the National DS8641 and DS3662 didn't quite meet the requirements. It is
unclear whether the
ones DEC used had been screened to better specs (either by National or DEC).