FTDI to USB adapter

[Marco Peele]

Hello

Trying to get my RC2014 ZED working but no luck with the FTDI connection i think

Bought a FTDI to USB adapter but i noticed that RX and TX are swapped?

(see picture attached)

Could this be the problem not getting a connection?

Thanks

Marco

[Spencer Owen]

Hi Marco,

Yes, the Tx and Rx are swapped on the Pi module so that the Micro USB Keyboard can plug in directly. If you plug the adapter in to the SIO/2 module then that should work fine.  Also note that the jumpers in that photo are set to "Pi" not "FTDI" so you won't get any output there anyway.

Hope that helps

Spencer

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[Marco Peele]

Hi

Removed the PI board and connected it to the SIO board,  but still nothing

I can see on the RX line activity on the scoop,  Level is 5v and drops down when pressing a key in the terminal

But TX is always high on 5 volt, nothing changes when pressing 'reset'

Pin 15 on the z84c4208 is also high

what  is the next step to troubleshoot?

Marco

Op vrijdag 29 januari 2021 om 15:33:12 UTC+1 schreef Spencer Owen:

[Spencer Owen]

Hi Marco,

I assumed from your first tweet that you already had your RC2014 up and running, and was just having trouble using it via the Pi module.  If it hasn't booted yet, then the first step is to take a really close look at all of the solder joints.  99% of RC2014s that don't boot seem to be down to a dodgy joint or jumper settings.  Luckily with the Zed there are hardly any jumpers to set wrong.  

If you've got your scope plugged in, then it's worth taking a brief look at each of the address and data lines.  All of those should show some kind of activity.  If any of them are permanently high, or low, or show mid-level voltages ( between about 1.5v - 3.5v) then that's where I would focus my attention.  Just use the minimum modules for now (Clock, CPU, ROM/RAM, Serial).

Having the Rx pin dip low when you type in to the terminal is to be expected.  That's the serial adapter which is doing that.  However, it should have some activity just after hitting reset, which would be the initial boot messages.  If you can see that kind of info on the scope but nothing on the terminal then it is probably down to the settings in your terminal software (Should be 115,200 baud, 8-N-1 assuming you're running it at 7.3728MHz)

Hope that helps point you in the right direction, but let us know how you get on.

Cheers

Spencer

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[Marco Peele]

Hi Spencer

All data lines show activity (5v)  and looks like your example on the troubleshooting guide using the scope

I have a 7.3 MHz signal, so clock should be working

I know that the RX line is working, i can see that on the scope,  checked is the cable is ok by shorting TX/RX on the adapter,  TeraTerm echos the character.  

Should the TX line drop to 0v when pressing the reset button? it stays at 5 v

after reset i can not see any activity the first few seconds

What circuit will keep this TX high so i can troubleshoot with the scope?

i will double check the soldering etc..

Marco'

Op zondag 31 januari 2021 om 13:01:41 UTC+1 schreef Spencer Owen:

[Tom Storey]

On Sun, 31 Jan 2021 at 13:43, Marco Peele <marco...@gmail.com> wrote:

Should the TX line drop to 0v when pressing the reset button? it stays at 5 v

after reset i can not see any activity the first few seconds

It should be high, because a transition to low would signal the start of a transmission to the receiver, which would then encounter an error or bogus data.

You can also check the CS pin of the SIO and see if it is being toggled after power on. If you're not seeing anything, perhaps the SIO is not being configured and/or no data is being sent to it which could indicate other issues (e.g. bad address decoding, or it is expected to be at another address).

[Marco Peele]

Hi

Still nothing on the TX line :-(

check the continuity and noticed one thing,  according to schematic pin 11 from the 74LS138 should connect to pin 35 (CE) of the Z84 SIO/2?

but there is no continuity

On which pin besides 14 i can check any further

Getting a little bit frustrated, sorry

Op maandag 1 februari 2021 om 12:17:32 UTC+1 schreef Tom Storey:

[Spencer Owen]

Hi Marco,

Yes, there certainly should be continuity between the '138 pin 11 and the SIO/2 pin 35.  This signal should normally be high, and it should drop down whenever the CPU wants to send or receive data to or from the SIO/2.  

So the easy solution would be to re-touch the solder joints on those the pins, and also remove and re-seat the chips, checking in case a leg is bent underneath.

The more interesting solution would be to hook your scope up to the '138 pin 11, and check that you see activity on that line shortly after reset.  This will be more than just sending out the initial boot message, but will also happen when the initialisation process writes to the registers on the SIO/2 and does other stuff.  If you don't see activity there then there may also be something further down the line that's causing other issues.  But, either way, you'll need to fix the continuity issue.

And to clarify the answer to your earlier question, no, the Tx line will not go low during a reset.  The only thing which is keeping Tx high is the SIO/2, and that will only wiggle it low when it is sending out data.

Hope that helps, but let us know how you get on.

Cheers

Spencer

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[Marco Peele]

Hi 

There is a signal on pin 11,  see attached image. 

Soldered a wire between the pin but still no luck. 

Is this signal on pin 11 correct ? 

Op 4 februari 2021 om 21:32:59, Spencer Owen (spe...@sowen.com) schreef:

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[Spencer Owen]

Hi Marco,

A admit that I have not actually probed that pin myself, and without all the other contextual data around what everything else is doing, it is impossible to say if that is correct. However... it does look just like what I would expect it to! During each of those low periods, the Z80 will either be talking to the SIO/2, or will be reading from it.

Out of curiosity, do you get the same results when you put the probe on SIO/2 pin 35?  I know you _should_ do, particularly if you have soldered a wire between them, but it is worth checking.

Also, if you set your scope to trigger when that signal goes low, do you get any data coming out of pin 25 or 26 of the SIO/2 (Port A Tx and Port B Tx)

Spencer

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[Marco Peele]

Hi

same result on pin 35,  but on pin 25/26 it is only high,  nothing changes when I press reset :-(

RX is working

regards

Marco

Op donderdag 4 februari 2021 om 22:14:07 UTC+1 schreef Spencer Owen:

[Spencer Owen]

Hi Marco,

It sounds like there is something else afoot with your machine. My suspicion is that there's a solder joint or two that's not quite right, although it could be something else. If you can post photos here of both sides of the boards, hopefully we can spot something that you may have missed.

Cheers

Spencer

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[Marco Peele]

Hi,

I suspect that the serial board is not functioning properly, i had to solder U1 directly to the board because the socket i get was for a 14 pin chip and not 16 pin

removed the solder and there was continuity between pin 11 of U1 and pin 35 on the SIO chip, after soldering i triple checked the joints but there is no continuity anymore

I can see a short burst on pin 11 of U1 after reset and the CF Busy led on the ROM card is flashing shortly but nothing on the TX pin

I am going to order a new dual serial card

Regards

Marco

Op zondag 7 februari 2021 om 15:57:27 UTC+1 schreef Spencer Owen:

[Marco Peele]

HI

Received the new dual serial board,  all immediate start working :-)

old board is defective I think

I can start playing with it

Regards

Marco

Op zaterdag 13 februari 2021 om 13:17:15 UTC+1 schreef Marco Peele: