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Messages - johnlon

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1
Discussion - Hardware / Re: UM245R baud rate
« on: January 20, 2021, 12:57:34 PM »
YEah it look like the baud rate is irrelevent - I have no idea why I was getting '?' anyway - thanks for the support

2
Discussion - Hardware / Re: UM245R baud rate
« on: January 20, 2021, 12:33:09 AM »
I tried both putty and the Adruino IDE serial monitor.
Both were receiving "?" as far as I could tell.
I put putty into logging mode and it just logged a load of bytes equivalent to ?.
This was for a few hours and I hadn't a clue how to make it work.

So then I saw someone mention 115k on a forum somewhere and tried that , and magically I was able to transmit back up to the PC, it had started working.

I then tried a faster speed in putty and that worked too.
So I saw the response here and then went back and tried 9600 as I had tried and failed using previously, and to my surprise it seemed to be working still.

I have no idea what happened.

3
Thanks.

So they can be programmed to pull low during USB suspend.

But can they be programmed to pull low when neither RD nor WR are asserted, ie when it's relinquished the bus?

4
Using the UM245R module which carries the FT245.
I hold the read and write lines high by default and only bring RD low to get the necessary -ve edge to make the data available - it must return high for RXF to reset.
I bring write low to clock out the data but the return it high again after at least 50ns. 
Seems to work.

5
I believe the UM245R has 200k pull ups on the D0-D7 data pins - is this correct?

When neither the read nor write control lines are enabled then I expect the data lines to go into a high impedance state with this weak 200k pull up  - is this all correct?

The bus that I am connecting the UM245R to already has a weak pull down, therefore I want to avoid a situation where the UM245R is pulling up and the surrounding circuit is pulling down - it's an irritating tug of war at the very least, but there is some more irritating impact in my circuit (see the post script).

Is there a means to either disaable the pull up entirely OR change the UM245R so that it pulls down instead of pulling up.

What are my options?

Thanks



PS. The impact of the 200k pull up in the UM245R is that an LED array that is directly attached to the bus lights up when nothing is asserting on the bus.
200K is enough on 5v to allow 15 to 20uAmp to flow and these LED's are really efficient and glow nicely at that current. I would rather thay were dark.
Of course I can use a 10k pull down to overcome the UM245R pull ups but that's a bit irritating.

6
Discussion - Hardware / UM245R - EPROM bus current limit setting
« on: January 18, 2021, 02:09:08 PM »
The UM245R documentation says that if I want self powered mode then I need to make a few specific wiring changes over the default USB powered.
In addition the doco says I also need to use the FT_Prog utility to change the EPROM from 'Bus Powered' to 'Self Powered'.

On the FT_Prog page where I change the power setting to "self powered" there is also a setting for the current that may be drawn from the bus.
It has a default of 100ma for the current draw from USB.

Does this actually limit the current draw by the device in some way - if so is there further doco and examples of how this is useful.

The documentaiton mentions "hybrid" power but doesn't give any indivation of how or where this mighty be useful.

Any further references?

7
The UM245R documentation says that if I want self powered mode then I need to make a few specific wiring changes over the default USB powered.
In addition the doco says I also need to use the FT_Prog utility to change the EPROM from 'Bus Powered' to 'Self Powered'.

I would like to understand what is the actual impact in the internal behaviour of the device when making this change?

If I make the wiring changes but forget to make the EPROM change to "Self powered" then will the device fail to work properly if I put it on self power?
And if so then what is it that actually causes the failure?

---

Can someone confirm that this eprom setting is purely informational to the host. If I leave it set to "Bus powered" but in fact run in self powered mode then what are the negative consequences if any. Are there in fact zero negative consequences???

8
Discussion - Hardware / UM245R baud rate
« on: January 18, 2021, 02:00:58 PM »
Hi where can I find documentation on defaults such as BUAD rate for this device.
By experimentation I was able to discover that the device worked ok at 115k but at 9600 which was the default for my serial terminal I got the usual '?' character instead.
I am using the VCP (com port) approach to talk to it.

Curiously I was able to transmit a single character at a time from the PC to the device over USB/VCP when using 9600, but was unable to communicate back to the PC from the UM245R without setting the serial terminal to 115k. I'm not clear why this might be.

But, more importantly where is the documentaiton covering such things as the speed / marity etc etc that need to be set.

Also is it possible to configure the UM245R to use different setting if needed (out of curiosity).


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