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:[email protected]] Sent: 31 March 2025 13:02 To: General Discussion: On-Topic and Off-Topic Posts <[email protected]> Cc: David Bridgham <[email protected]> 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
