Yet another MK14 vdu card

[SiriusHardware]

Just had a preliminary test and play - must say the 32-way edge connector on the assembly is a really firm fit so any fears I might have had about ZX-style add-on wobble were well and truly groundless.

I fired it up in character mode without loading anything and was surprised to see that about half of the random characters on the screen were randomly in inverse, so I realised Realtime must have incorporated Tim's 'single character inversion' mod into Realview and proved that this was indeed the case by navigating to address 0200 and entering first a few instances of 0x20 (which displayed as black character squares, ie, 'Space'), followed by a few instances of 0xA0 - the same character code but with bit 7 set, and they came up as white squares (inverted spaces). I don't think I saw this mentioned anywhere in the document and so to have this built in is an unexpected bonus.

[Realtime]

Great that you’ve got RealView plugged in and displaying. I realised yesterday that I had forgotten to document the Bit7 character inversion in the Tech Notes so will add it in the update.

WRT the 330R resistors, I’m wondering if they are needed now that there are 1K protection resistors in the TOPPAGE signal path? Will have a proper look when I’m more awake.

[Realtime]

Originally Posted by SiriusHardware

If we route TOP PAGE to MK14_PS3 either permanently or via a switchable arrangement, should we also make the same change on the MK14_PS3 line, that is, insert a 330R resistor in series with the BAT48 diode on MK14_PS3?

I agree with you, add a 330R resistor in series with the diode currently in position SW2-3 / SW2-18, providing protection for TOPPAGE if PS3 is grounded by SW1.

[SiriusHardware]

Actually when you said this:

WRT the 330R resistors, I’m wondering if they are needed now that there are 1K protection resistors in the TOPPAGE signal path?

I thought that might be the better way to go, something like the illustration below. A limit / safety resistor between the TOP PAGE output of the CPLD and everything else.

The illustration shows only one complete 'channel' of control, with the arrowed connections leading off from the other switches / links assumed to go to other identical channels.

Case 1: TOP_PAGE is high and grounding switch is closed and / or 8154 pin is in output mode and is LOW - voltage difference falls across 1K resistor so no damage to TOP PAGE or 8154 port pin.

Case 2: TOP_PAGE is LOW or the grounding switch is closed and the 8154 pin is in output mode and set HIGH - BAT48 blocks the pulldown of 8154 pin so the 8154 pin is not forced low, so not damaged.

For each additional channel switched to be driven by TOP_PAGE there will be another parallel 3K9 resistor trying to keep the lines high, so it may be necessary to raise the value of the pullup resistors a little so that TOP_PAGE (via 1K) can always reliably pull the control lines low even when up to three are being driven by TOP_PAGE.

[Brian of Romsey]

Hi, a first time poster here. This may initially seem a bit OT, but bear with me. I'm planning (next nine months when I and my old stuff are happily in the same country) to build some RETRO kit. I'll get my SC/MP II and an old 6809 going. My plan is for my own 64 way bus, using generally Eurocard dimensions and DIN41612 connectors. Initial efforts my be only 100 mm by 100 mm to get el-cheapo PCBs from China. So to the relevant part. I'm thinking a+b connectors, so that they can be replaced by dual row pin headers for prototyping. Does anyone know of a source of all-connected, nothing assumed back-planes for DIN41612 a+b? Or even back-planes that maybe make some assumptions about power and ground?
I saw the 'planar' back-planes by Scott Baker on YouTube https://youtu.be/SvSKPFVnW94?t=718 He has also made 3-way triangle and 5-way pentagon versions https://www.smbaker.com/wordpress/wp...ver-5board.jpg. Has anyone here done anything similar? Note that these planar back-planes are quite complicated to route, as the signals have to (in the case of the 4-way) go from left (top) to bottom (left) to right (bottom) and then to top (right). And so on along each connector.

[Mark1960]

You could possibly try Chris oddy’s 10 slot unbuffered backplane for Acorn eurocard systems.
http://www.theoddys.com/acorn/Replic...ca_boards.html

If you follow the Acorn pin definitions you might also be able to use some of his other replica cards.

If you like strange backplanes there is also this one I made, though I still haven’t finished the boards to go in it.
https://groups.google.com/g/rc2014-z...m/TLXN2PoKAwAJ

[Brian of Romsey]

Originally Posted by Mark1960

You could possibly try Chris oddy’s 10 slot unbuffered backplane for Acorn eurocard systems.
http://www.theoddys.com/acorn/Replic...ca_boards.html

If you follow the Acorn pin definitions you might also be able to use some of his other replica cards.

If you like strange backplanes there is also this one I made, though I still haven’t finished the boards to go in it.
https://groups.google.com/g/rc2014-z...m/TLXN2PoKAwAJ

Strange is the word! I wonder if the flexible PCB thing that China does nowadays might have been a better option.

Ta for the pointer to Chris Oddy's site. I reckon the 5-slot will do me nicely (for a mere £8 delivered to Cambridge). His back planes are effectively 63 way with just a32 and b32 connected together. I can make this work for me.

Cheers, Brian.

[Mark1960]

I didn’t think Chris had a five slot.

One other option would be to use one of the RC2014 backplane boards that are designed for 2x40 pin headers, just pick a position to mount the 32 a+b connector within the 2x40. Steve Cousins has a few variations in easyeda with the connectors on 0.6 inch centres. These have power and ground on both rows at pin 17 and 18 of the 2x40 connectors.

https://oshwlab.com/sccousins/sc113-backplane

[ChrisOddy]

Oh yes I do !, its a recent addition as part of the FileStore project.

Chris

[Brian of Romsey]

Originally Posted by Mark1960

I didn’t think Chris had a five slot.

One other option would be to use one of the RC2014 backplane boards that are designed for 2x40 pin headers, just pick a position to mount the 32 a+b connector within the 2x40. Steve Cousins has a few variations in easyeda with the connectors on 0.6 inch centres. These have power and ground on both rows at pin 17 and 18 of the 2x40 connectors.

https://oshwlab.com/sccousins/sc113-backplane

I had already had a bit of a look at RC2014 back planes. They aren't quite as pure/neutral as I wanted. Which is why Chris Oddy's are great for me.