31 Mar
2025
31 Mar
'25
2:42 p.m.
David
The SOT-23 wide per output signal is a useful metric, thankyou. I presume that is with
outputs drivers on both sides.
Your comparator ask is probably unobtanium:
- OC output => slow (75+ ns, just like the Unibus settling time - although perhaps
largely due to an initially overdriven )
- 3v3 operation => beyond the rails operation with 5v logic; Google says Maxim do some
parts, rails +/- 0.3 v -- just like TI, who are more honest by omiting the BTR sticker
Should you find such a beast, I'd like to know.
Best Wishes
Martin
-----Original Message-----
From: David Bridgham via cctalk [mailto:cctalk@classiccmp.org]
Sent: 31 March 2025 13:02
To: General Discussion: On-Topic and Off-Topic Posts <cctalk(a)classiccmp.org>
Cc: David Bridgham <dab(a)froghouse.org>
Subject: [cctalk] Re: DEC bus transceivers
On 3/30/25 6:44 PM, Martin Bishop wrote:
Your driver design sketches and comments are
substantially on the money. Thank you for making them public. However, an effective
implementation in discrete components would not be "tiny" - even with 0402
passives and a pick / place machine on the case.
No, not tiny. With the BGA parts of the FPGA and DDR3 SDRAM, I'd already made the
choice that this board would have to be commercially assembled so smaller parts were
acceptable. Even so, at one point I mocked it up just to see if it would fit with SOT-23
and 0603 parts and it did, just barely, across a double-height QBUS board. That was one
of my simpler designs for this, though. So dunno. If you can lay out the circuit to
drive two bus lines in a chain of components that's only one
SOT-23 wide, then I think it fits. It might stretch up the board a ways, but I have room
in that direction.
Perhaps someday, someone will do a Q/U driver on a
multi project wafer - or is that unafordable. Or, to fly another kite - what about FPAA
(Field Programmable Analog Array) components ?
I hadn't thought about those multi-project wafers. Don't know if that'd make
sense. I keep hoping that one day soon we'll start to see hobbyist-level 3d printing
of ICs. Maybe only 1µm feature size or even larger but think what people would do with
that. Not out there yet though.
Regarding comparators, as receivers, the TLV3501 (for
example) is a 5v / 5 ns part - add hysteresis and set the H/L thresholds using resistors.
Certainly receives OC signals for me.
Yup, that's the sort of part I was thinking of. I'd used the MAX9107 but the TI
part is even faster. One thing I could never find was a comparator that was both fast and
had a OC/OD output. Or one that ran on 3.3V so it could drive the FPGA directly but was
rated for higher voltages than Vcc on the inputs.
Should you make further progress very interested to
hear of it
I'm not sure where I'm going to go with these ideas but if I do anything, I'll
be sure to let people know.
Dave