I2C 4 U

for bbc micro/electron hardware, peripherals & programming issues (NOT emulators!)
Post Reply
User avatar
MartinB
Posts: 4980
Joined: Mon Mar 31, 2008 9:04 pm
Location: Obscurity
Contact:

I2C 4 U

Post by MartinB » Tue Apr 12, 2016 8:36 pm

I sense another mega-thread coming on.... :shock: :-k :wink:

I've been working on my next Beeb project for about a year now all told and think I'm just about ready to release something for testing. That's obviously not a solid year's work of course, far from it, just a year of the usual 'what's-left-over' hobby time. In the end, this is really all just software, a rom actually, and apart from a bit of cable, it'll be a virtual freebie other than whatever you fancy in the way of some cheapo ebay grabs - more of which later. Most of all though, forget the technical stuff, I think this promises to really great FUN! \:D/ :D

(To be fair, there is actually plenty of potential for serious stuff too...... :roll: )

Being me, the project of course involves the ubiquitous User Port and even more predictably from me, some ubiquitous bit-banging - oh how I love bit banging... =P~. If you're into Arduino, Pi's and the like, (of which I myself have none), you may already be familiar with this stuff but hopefully now, the Beeb can join the party too! :D

Anyway, I'm sure there's going to be lots to talk about over time so I'll leave the remainder of the intro to a Shaky-Cam video production - pull up a sand-bag, grab some popcorn and we shall begin.....



Here's what the first release of the rom will offer...
i2c rom help.png
I'm a bit busy with all manner of things at the moment but I should between times be able to take questions from the floor if there are any. I'll aim to push the rom out as soon as possible for testing but I need to knock up some basic instructional info together with some cable details although the latter is easy being just four wires connected to the User Port.
Last edited by MartinB on Mon Jul 09, 2018 8:19 pm, edited 1 time in total.

User avatar
danielj
Posts: 6650
Joined: Thu Oct 02, 2008 4:51 pm
Location: Manchester
Contact:

Re: I2C 4 U

Post by danielj » Tue Apr 12, 2016 8:43 pm

=D> Loving it :D - I particularly like the potential for making a "Someone's trying to pinch my beeb" sensor. (My imagination isn't very good at this time of the evening!)

User avatar
sirmorris
Posts: 751
Joined: Wed Feb 11, 2009 12:18 pm
Location: oxfordshire uk
Contact:

Re: I2C 4 U

Post by sirmorris » Tue Apr 12, 2016 9:05 pm

=D> genius! =D>

User avatar
CMcDougall
Posts: 6304
Joined: Wed Feb 02, 2005 3:13 pm
Location: Shadow in a Valley of Scotland
Contact:

Re: I2C 4 U

Post by CMcDougall » Tue Apr 12, 2016 9:07 pm

great little things from China for the price of a stamp and envelope :P

at last, I can put that white box thing with nWii written on it to some proper use! =D> :lol:
(got every game for it on extHD, but its crap, kids bored of it too :roll: )

PS where are your famous gloves gone in the vid :shock: :?
ImageImageImage

User avatar
paulv
Posts: 3716
Joined: Tue Jan 25, 2011 6:37 pm
Location: Leicestershire
Contact:

Re: I2C 4 U

Post by paulv » Tue Apr 12, 2016 10:12 pm

That looks great Martin I2C is good fun and already built in on the Arc so I had a great time reverse engineering its use to support the Watford VIDC Enhancers.

I've actually been working on a small PCB for the Arcs to do a little CMOS chip replacement board with I2C breakout on it. I've been meaning to publish the eagle files here but been laid low with a tummy bug for the last couple of weeks :( :twisted:

Spurred on by this, I might just dig the files out and publish them now :D

Paul

waltermixxx
Posts: 241
Joined: Wed Jan 14, 2015 4:18 pm
Location: Toronto
Contact:

Re: I2C 4 U

Post by waltermixxx » Wed Apr 13, 2016 1:57 am

Very excited to see where this goes. :)

Cheers. :)

User avatar
flibble
Posts: 666
Joined: Tue Sep 22, 2009 10:29 am
Contact:

Re: I2C 4 U

Post by flibble » Wed Apr 13, 2016 2:17 am

great little things from China for the price of a stamp and envelope :P
It's awesome, I've really gotten into i2c on my raspberry pi (under linux), so many little devices for not much money (a quid or 3).

Things I've got working,

2x16 character LCD display
128x64 pixel OLED display
temperature/humidity sensor
pcf8574 8 GPIO pin boards
4x7 segment display LED clock display
256KB EEPROM chip

It'll be fun to see if I can make any work on the beeb :)

(I still have a DAC board and a accelerometer/gyroscope board to get working on the pi)

User avatar
sweh
Posts: 1969
Joined: Sat Mar 10, 2012 12:05 pm
Location: New York, New York
Contact:

Re: I2C 4 U

Post by sweh » Wed Apr 13, 2016 2:49 am

Heh, your ROM is blatting directly into BASIC integer variables? Funky :-)
Rgds
Stephen

User avatar
MartinB
Posts: 4980
Joined: Mon Mar 31, 2008 9:04 pm
Location: Obscurity
Contact:

Re: I2C 4 U

Post by MartinB » Wed Apr 13, 2016 6:22 am

@ Charlie - well, amongst geniuses such as yourself, I'm not sure about that but I'm glad someone thought of this even it was me! I love tinkering with these thrupenny gadgets so the I2C interface is a perfect route to lots of fun... :D

@ Colin - normally, by April, the gloves have gone but in fact, I was actually still wearing them (still more like mid-winter :roll:) and only slipped them off to do the Shaky-Cam because I don't like handling delicate electronics with mitts on. (Bound to be some static-inducing synthetics in there I suspect.... :shock:)

@ Peter - Agreed, awesome fun =D>. As far as I'm concerned, there's no reason why they won't all work - you can do everything with the Beeb rom commands that any I2C Master can do and I've catered for things like clock-stretching so fill yer boots I say!

The only caveat on devices is that they must use a 5v Vcc external supply having an on-board 5v_to_3.3v regulator. If you have a 3.3v gadget that you want to use, there are dozens of simple £1.50 (or less!) I2C level converters on ebay or Amazon that you can place in series with your gadgets such as the example below. All the devices that I have bought so far have had the on-board regulation so 5v Vcc does seem to be a popular and readily available configuration.

Image

@ Stephen - I have written the I2C commands to principally use the RS232 buffer page at $0A00 for data in and out because that makes logical sense with both interfaces being serial. Additionally though, to make the commands far more flexible for everyone and increase the accessibility for users who are not quite so comfortable with assembler or even peeking and poking, I decided to allow every parameter (i.e. device address, device register and the data parameter) to be specified directly as any of Basic's 26 resident integer variables (so A%-Z%) because on all the target machines with Basic-in-rom, (Beeb B, Master, Elk, Compact), the location in memory of these variables is common and fixed. Hence, they can be addressed directly noting that the bottom eight bits only (the LS Byte) of each are used and the higher three bytes are ignored. I know this will make the Acorn police have an anger spike but to fair, I have written to Acorn to ask when Basic III and OS1.3 are due for release and they simply haven't responded. So, if you like assembler and manual memory manipulation, just ignore the Basic % variable options and specify everything explicitly in hex. In this way and without me losing too many hours of my life, all preferences are covered. Personally, I'm thoroughly enjoying playing with I2C gadgets from Basic and using the % var facility because it's so simple to get to the fun! =D> :D
.
.
.
Attachments
i2c regulator.png
i2c regulator.png (86.26 KiB) Viewed 1409 times

User avatar
daveejhitchins
Posts: 4460
Joined: Wed Jun 13, 2012 5:23 pm
Location: Newton Aycliffe, County Durham
Contact:

Re: I2C 4 U

Post by daveejhitchins » Wed Apr 13, 2016 8:09 am

Excellent work, as usual, Martin . . . =D>

I'll have to dig out my I2C ANDI Odual (Analogue & Digital I/O interface and our take on Podual!) - I'm sure I still have the prototype(?). We made this specifically for School/Hobbyist use. We had an I2C connector on some of our A3000 interfaces.

Dave H :D
Last edited by daveejhitchins on Sat Aug 26, 2017 9:13 am, edited 1 time in total.
Parts: UM6502CE, GAL22V10D, GAL16V8D, AS6C62256A, TC514400AZ, WD1772, R6522, TMS27C512, AT28C256
Products: ARA II, ARA III, ABR, ATI, AP6, MGC, AP5 . . .
For a price list, contact me at: Retro Hardware AT dave ej hitchins DOT plus DOT com

User avatar
1024MAK
Posts: 8000
Joined: Mon Apr 18, 2011 4:46 pm
Location: Looking forward to summer in Somerset, UK...
Contact:

Re: I2C 4 U

Post by 1024MAK » Wed Apr 13, 2016 9:49 am

Martin, I knew you were up to something, as you had gone a bit quiet.

That I2C set-up look like more excellent work from you :D

Please do carry on :mrgreen:

Mark

User avatar
TheCorfiot
Posts: 657
Joined: Mon Jan 08, 2007 5:22 pm
Contact:

Re: I2C 4 U

Post by TheCorfiot » Wed Apr 13, 2016 9:27 pm

Martin thank you so much...
I2C controlled by the Beeb, this is awesome.

:)

User avatar
1024MAK
Posts: 8000
Joined: Mon Apr 18, 2011 4:46 pm
Location: Looking forward to summer in Somerset, UK...
Contact:

Re: I2C 4 U

Post by 1024MAK » Wed Apr 13, 2016 9:54 pm

TheCorfiot wrote:I2C controlled by the Beeb, this is awesome.
Or maybe the Beeb controlled by a I2C device (Microcontroller maybe?)... :shock: :D :lol:

Mark

User avatar
MartinB
Posts: 4980
Joined: Mon Mar 31, 2008 9:04 pm
Location: Obscurity
Contact:

Re: I2C 4 U

Post by MartinB » Wed Apr 13, 2016 10:12 pm

TC wrote:I2C controlled by the Beeb, this is awesome.
It really is too - I've been having so much fun playing that I've got to keep nudging myself back on task to get the rom released for test by all you wonderful people :) (A barometer module arrived today so I've just been having fun predicting tomorrow's weather.... =D> )
Mark wrote:Or maybe the Beeb controlled by a I2C device (Microcontroller maybe?)... :shock: :D :lol:
:shock: By a curious coincidence, I'm just in the middle of typing a long post all about that! Watch this space..... :wink:

User avatar
MartinB
Posts: 4980
Joined: Mon Mar 31, 2008 9:04 pm
Location: Obscurity
Contact:

Re: I2C 4 U

Post by MartinB » Wed Apr 13, 2016 10:32 pm

If you don't do technical, ignore this, it won't matter to you other than determining which User Port pins the four wires of your I2C cable need to go to.... :wink:

Before I commit to the final cable design (ha! four wires :lol:), I've decided to change the physical User Port connections from the current 2xPB lines, one for the clock (SCL) and one for the data (SDA), to 1 PB line for SDA and CB2 for SCL. I originally chose PB lines because as an I2C Master, you need to able to recognise if a Slave device has declared itself busy by its remotely holding the clock line low. This is known as clock-stretching and it is important to be able to detect this behaviour for slow or heavily processed slave devices. I therefore initially steered away from CB2 because (a) I couldn't see how you could read the CB2 steady level like you can for a PB line and (b) why use CB2 when a PB line will do just fine!

Well, as an I2C Master, the Beeb is in control of the clock and initiates all transfers on the I2C bus meaning it doesn't have to do any polling of the clock or data lines. However, I'm thinking now that it would be cool down the line to expand the rom functionality to allow the Beeb to optionally be a Slave device too because then it would be really easy to use say an RPi (if you have one - what is one of those btw? :? :-k) to do things like software downloads to, or memory uploads from, the Beeb. It would also allow for example, two I2C-equipped Beebs to talk to each other.
Now, if we were to do this, I'm pretty sure that we'd want to be interrupt-driven to wake up on an I2C clock edge. I couldn't do this for UPURS because the interrupt latency of a 2MHz 6502 (in an OS1.2 shell) is way to poor for a fast asynchronous serial link such as 115k RS232 and hence I had to get into some serious cycle-counting design. However, I think I'd rather at least have the option of interrupts for I2C and although it's only needed for Slave operation (that I haven't written yet!), it'll be better to get the cable configuration correct now.

Now, all the 6522 CB2 functionality is predicated on edge transitions and not on levels but even so, after an extended play tonight, I've figured out how to do what's needed and so I'm doing a quick re-work of the clock control code for some testing tomorrow.

Since supporting information will be on a drip feed for this project, it's probably worth mentioning at this stage that the reason that a 6522 Port B (PB and CB lines) are suitable for I2C is because of the internal hardware arrangement of the port IO stage. I2C is unusual (and herein lies its cleverness) in that any device, Master or Slave, only drives the clock and data lines to the low state, the high state being achieved by the active devices going high impedance leaving the all-important pull-up resistors to lift the line to the high state. For this functionality, I2C devices therefore need to have an Open-Drain output stage such that they can be pulled high without harm. We are therefore fortunate that the 6522 has just a stage on its PB port and it also has internal pull-ups of about 1k ohm which is a little on the low side (actually bottom end of the I2C spec.) but, as you have witnessed, it works just fine :D

Anyway, enough waffle for now, more next time and perhaps the initial rom release tomorrow or Friday....

User avatar
sweh
Posts: 1969
Joined: Sat Mar 10, 2012 12:05 pm
Location: New York, New York
Contact:

Re: I2C 4 U

Post by sweh » Wed Apr 13, 2016 10:38 pm

MartinB wrote: @ Stephen - I have written the I2C commands to principally use the RS232 buffer page at $0A00 for data in and out because that makes logical sense with both interfaces being serial. Additionally though, to make the commands far more flexible for everyone and increase the accessibility for users who are not quite so comfortable with assembler or even peeking and poking, I decided to allow every parameter (i.e. device address, device register and the data parameter) to be specified directly as any of Basic's 26 resident integer variables (so A%-Z%) because on all the target machines with Basic-in-rom, (Beeb B, Master, Elk, Compact), the location in memory of these variables is common and fixed. Hence, they can be addressed directly noting that the bottom eight bits only (the LS Byte) of each are used and the higher three bytes are ignored. I know this will make the Acorn police have an anger spike but to fair, I have written to Acorn to ask when Basic III and OS1.3 are due for release and they simply haven't responded.
Woah. No need to be so defensive. I merely said it was funky, because it _is_.

(BTW, there's also @% which lives at &400 - a variable most people forget about!).
Rgds
Stephen

User avatar
MartinB
Posts: 4980
Joined: Mon Mar 31, 2008 9:04 pm
Location: Obscurity
Contact:

Re: I2C 4 U

Post by MartinB » Wed Apr 13, 2016 10:45 pm

Lol - no worries Stephen, I was only being defensive because I'm not from a software background and I've had some bad experiences on here so I saw a good opportunity to get in first and explain how and why I'd implemented this I2C rom functionality... :wink: 8)

I deliberately skipped @% because it has specific uses in Basic and I didn't want for example I2C to be capable of screwing up Basic's screen print formatting :)

User avatar
paulv
Posts: 3716
Joined: Tue Jan 25, 2011 6:37 pm
Location: Leicestershire
Contact:

Re: I2C 4 U

Post by paulv » Wed Apr 13, 2016 11:04 pm

daveejhitchins wrote:Excellent work, as usual, Martin . . . =D>

I'll have to dig out my I2C ANDI Odual (Analogue & Digital I/O interface and our take on Podual!) - I'm sure I still have the prototype(?). We made this specifically for School/Hobbyist use. We had an I2C interface on some of our A3000 interfaces.

Dave H :D
... and A300 interfaces too like this one.

Paul

User avatar
flaxcottage
Posts: 3303
Joined: Thu Dec 13, 2012 8:46 pm
Location: Derbyshire
Contact:

Re: I2C 4 U

Post by flaxcottage » Thu Apr 14, 2016 6:20 am

MartinB wrote:However, I'm thinking now that it would be cool down the line to expand the rom functionality to allow the Beeb to optionally be a Slave device too because then it would be really easy to use say an RPi (if you have one - what is one of those btw? :? :-k) to do things like software downloads to, or memory uploads from, the Beeb.
This looks like an exciting possibility - a Raspberry Pi fileserver for a BBC (or any 6522-equipped system for that matter - a UK101 for instance) based on a Pi zero and driven by I2C. :D More on Saturday at the WROCC show. :wink:
- John
Image

User avatar
MartinB
Posts: 4980
Joined: Mon Mar 31, 2008 9:04 pm
Location: Obscurity
Contact:

Re: I2C 4 U

Post by MartinB » Thu Apr 14, 2016 6:28 am

flaxcottage wrote:...based on a Pi zero and driven by I2C. :D More on Saturday at the WROCC show. :wink:
Whoops! Have you produced a Beeb I2C interface too ? (If so, I hope I haven't stolen your thunder...?)
Paul wrote:.. and A300 interfaces too
That probably gives the Arc an I2C Master capability only (or 'Microcontroller' in official I2C parlance) which highlights why I want to give the Beeb Master and Slave capability allowing connection of the two together. It is actually possible and allowed to have two (or more) Masters on a given I2C bus but that then requires each to have extra bespoke arbitration functionality to handle 'collisions' (to use a modern word) which at this time I haven't embodied.

User avatar
tricky
Posts: 2849
Joined: Tue Jun 21, 2011 8:25 am
Contact:

Re: I2C 4 U

Post by tricky » Thu Apr 14, 2016 7:12 am

I love everything you do for the beeb, and I don't mean to sound ungrateful, but now I have MMC, I don't want to give it up [-o<
If you had used 2 PB lines, would it have been possible to have both connected at the same time?
I actually use SmartSPI on my beebs, one has STL RAM (PB0-2), MMC (PB4-5) and a space PB6-7 for something new :D

User avatar
daveejhitchins
Posts: 4460
Joined: Wed Jun 13, 2012 5:23 pm
Location: Newton Aycliffe, County Durham
Contact:

Re: I2C 4 U

Post by daveejhitchins » Thu Apr 14, 2016 7:16 am

paulv wrote:... and A300 interfaces too like this one.
Crikey, I'd forgotten all about that one :oops: Don'e suppose anyone has one, so I can 'capture' the design'?

Dave H :D
Parts: UM6502CE, GAL22V10D, GAL16V8D, AS6C62256A, TC514400AZ, WD1772, R6522, TMS27C512, AT28C256
Products: ARA II, ARA III, ABR, ATI, AP6, MGC, AP5 . . .
For a price list, contact me at: Retro Hardware AT dave ej hitchins DOT plus DOT com

User avatar
paulv
Posts: 3716
Joined: Tue Jan 25, 2011 6:37 pm
Location: Leicestershire
Contact:

Re: I2C 4 U

Post by paulv » Thu Apr 14, 2016 7:23 am

daveejhitchins wrote:
paulv wrote:... and A300 interfaces too like this one.
Crikey, I'd forgotten all about that one :oops: Don'e suppose anyone has one, so I can 'capture' the design'?

Dave H :D
Ummmm... That one is mine.... I'll PM you.

Paul

User avatar
daveejhitchins
Posts: 4460
Joined: Wed Jun 13, 2012 5:23 pm
Location: Newton Aycliffe, County Durham
Contact:

Re: I2C 4 U

Post by daveejhitchins » Thu Apr 14, 2016 7:24 am

@Martin . . . Will it be Electron compatible at any time? I could, fairly quickly, prepare the cartridge version of the user port, as it's been in the pipeline for some time now.

I had planned to use two identical connectors (to access both ports), however, they won't fit. So, instead, I was planning a DIN connector (similar to an RS423 cartridge I've seen). This could then be used for User Port, I2C and UPURS :D

Dave H :D
Parts: UM6502CE, GAL22V10D, GAL16V8D, AS6C62256A, TC514400AZ, WD1772, R6522, TMS27C512, AT28C256
Products: ARA II, ARA III, ABR, ATI, AP6, MGC, AP5 . . .
For a price list, contact me at: Retro Hardware AT dave ej hitchins DOT plus DOT com

User avatar
MartinB
Posts: 4980
Joined: Mon Mar 31, 2008 9:04 pm
Location: Obscurity
Contact:

Re: I2C 4 U

Post by MartinB » Thu Apr 14, 2016 9:55 am

@ tricky - Hey, don't be afraid to ask these things, that's why I like developing on threads so everyone can at least make suggestions, even if I ignore them! :lol:

This is indeed a congested connector and all I can say at the moment is that I have to use a 5v and a 0v line together with CB2 for the I2C clock, the reason for the latter I explained in my earlier post. For the remaining PBn line, I can make that whatever but the reason I've selected PB0 is two-fold - (1) because this line is only a single bit shift from the Carry and (2), more significantly actually, because with the other three connections, it permits the option of a neat narrow cable with just the right-hand 6 cores being needed. I don't think concurrent device connection, i.e. multiple things hanging off a given line, is a good idea - off the top of my head, I'm sure there would be loading and cross-communication issues. I don't actually have any of the other gadgets you are referring to and so I don't have a problem myself but I'm certainly open to suggestions on this..... 8)

@ Dave H - It's already up and running on the Elk as written without issue, just requires a User Port (EUP in my case) and an I2C rom version built for the different 6522 base address of $FCB0. (I'll push out a bespoke Elk version in the short term rather than a universal.) Because I2C is synchronous and there are no constraints on maximum clock periods or duty cycles, the Elk's quirky timing doesn't cause any problems.
User Port.png
Last edited by MartinB on Thu Apr 14, 2016 1:15 pm, edited 1 time in total.

User avatar
sydney
Posts: 2249
Joined: Wed May 18, 2005 9:09 am
Location: Newcastle upon Tyne
Contact:

Re: I2C 4 U

Post by sydney » Thu Apr 14, 2016 10:53 am

tricky wrote:I love everything you do for the beeb, and I don't mean to sound ungrateful, but now I have MMC, I don't want to give it up [-o<
If you had used 2 PB lines, would it have been possible to have both connected at the same time?
I actually use SmartSPI on my beebs, one has STL RAM (PB0-2), MMC (PB4-5) and a space PB6-7 for something new :D
I'm pretty sure it would be possible to fit an additional 6522 to a beeb using the econet connections. It would jus t be a case a finding them on the pcb and connecting them to a 6522. This would enable you to have your mmc connected at the same time. Or you could build sweh's 1mhz bus dual 6522 expansion.

User avatar
sweh
Posts: 1969
Joined: Sat Mar 10, 2012 12:05 pm
Location: New York, New York
Contact:

Re: I2C 4 U

Post by sweh » Thu Apr 14, 2016 5:12 pm

tricky wrote:I love everything you do for the beeb, and I don't mean to sound ungrateful, but now I have MMC, I don't want to give it up [-o<
If you had used 2 PB lines, would it have been possible to have both connected at the same time?
I actually use SmartSPI on my beebs, one has STL RAM (PB0-2), MMC (PB4-5) and a space PB6-7 for something new :D
You could always create a 2nd (and 3rd) user port at different addresses, using the 1Mhz bus :-) http://sweh.spuddy.org/Beeb/2nd_User_Port/

In theory, UPURS, MMC and I2C all at the same time :-)
Rgds
Stephen

User avatar
MartinB
Posts: 4980
Joined: Mon Mar 31, 2008 9:04 pm
Location: Obscurity
Contact:

Re: I2C 4 U

Post by MartinB » Thu Apr 14, 2016 6:28 pm

I've finished testing the re-worked rom and it now uses CB2 for the I2C SCL clock line and it's all good. As is stands then, this is my proposed configuration for I2C on the User Port...
I2C User Port Connections.png
As I said earlier in response to tricky's (perfectly reasonable) thoughts, my proposal works well because the four wires are grouped and contiguous in the ribbon cable so the latter can be cut down to quite a neat and manageable affair. I'm just about ready to release the first test version of the rom (now v0.2) so this does ideally need to be resolved before people dash off to make cables but I'm reluctant to change my proposal for the reasons I've outlined. In the absence of a User Port Pin Allocation Committee to adjudicate on this, what does everyone think...?

[ My own feeling on this is that for folk who want to have multiple devices instantly available, someone perhaps need to think about producing something along the lines of a User Port switch box with a single connection to the Beeb and say four copies of the connector on the box where one of the four can be selected via a switch.]
Last edited by MartinB on Thu Apr 14, 2016 6:35 pm, edited 1 time in total.

User avatar
sweh
Posts: 1969
Joined: Sat Mar 10, 2012 12:05 pm
Location: New York, New York
Contact:

Re: I2C 4 U

Post by sweh » Thu Apr 14, 2016 6:35 pm

MartinB wrote:what does everyone think...?
IMHO, you should design the cable as if it was the only thing on the port. The userport was only designed for one thing at a time, after all :-)
MartinB wrote:[ My own feeling on this is that for folk who want to have multiple devices instantly available, someone perhaps need to think about producing something along the lines of a User Port switch box with a single connection to the Beeb and say four copies of the connector on the box where one of the four can be selected via a switch.]
Before I created my 2nd UserPort I did something similar to this. It's fortunate that many of the userport lines are ground, so I was able to use a cheapo printer-port switcher and just make some DB25->UP connector cables.

You can see it on the middle Beeb in this picture http://sweh.spuddy.org/Beeb/Images/grow ... ection.jpg (one port was UPURS, the other was TurboMMC). It worked...

The problem with this is that switching devices may require BREAK or even CONTROL-BREAK because of the device isn't present on reset then the controlling ROM may not initialise. It was too annoying; I couldn't transparently switch between HostFS:UPURS and MMC.
Rgds
Stephen

User avatar
1024MAK
Posts: 8000
Joined: Mon Apr 18, 2011 4:46 pm
Location: Looking forward to summer in Somerset, UK...
Contact:

Re: I2C 4 U

Post by 1024MAK » Thu Apr 14, 2016 6:46 pm

As chair of the newly formed UPPARCE (User Port Pin Allocation Recommendation Committee Executive) I cannot be party to such a vote by non-committee members!

It is the responsibility for each designer to register his/her design and intentions to the UPPARCE. Once received, the UPPARCE will investigate, drink, eat and may finally adjudicate on this.

Mark
UPPARCE Chair

Bribes accepted only at our overseas tax haven bank :lol:

Post Reply