Jump to content
42bs

ComLynx<->USB Adapter

Recommended Posts

Hi, since RS232 is mostly gone in modern PCs, I wanted to use one of the many USB<->TTL adapters.

Looking around there are many with a Prolific chip, some with CP2022 and also some with FTDI.

 

Prolific is bad, as these allow only the "standard" baudrates. But CP2022 accepts also the Lynx-Baudrate of 62500Bd!

Important: Most TTY examples check only for those standard baudrates. But Windows sends _any_ down to the driver.

Reading back returns the actual baudrate used!

 

Important is, that those chips are 5V tolerant, so there is no level-shifter needed!

 

The straight forward connection GND to GND ComLynx RX/TX to RX/TX of the CP2022 works for sending from PC to Lynx, but not from Lynx to PC. One needs a small (Schottky) diode from ComLynx to TX (see gfx).

 

post-3110-0-37194700-1520685306.png

 

I used just a small SMD diode I found on some old PCB. With this, data transfer with 62500Bd works perfect.

 

Cheers

Edited by 42bs

Share this post


Link to post
Share on other sites

I found a already equipped board with a dual interface using this chip:

https://www.silabs.com/documents/public/data-sheets/CP2105.pdf

 

Nice thing, you can connect two lynx at one USB cable. but only one of the connections features "unusual" speeds like 31250 and 62500.

 

Annoying thing, shipping is more expensive that the boards :-(

 

42bs: I was wondering about the diode. its clear that it prevents the TX from pulling the line while the lynx is sending. but wouldnt a resitor do a better job?

Share this post


Link to post
Share on other sites

I found a already equipped board with a dual interface using this chip:

https://www.silabs.com/documents/public/data-sheets/CP2105.pdf

 

Nice thing, you can connect two lynx at one USB cable. but only one of the connections features "unusual" speeds like 31250 and 62500.

 

Annoying thing, shipping is more expensive that the boards :-(

 

42bs: I was wondering about the diode. its clear that it prevents the TX from pulling the line while the lynx is sending. but wouldnt a resitor do a better job?

 

You mean two Lynx'es w/o ComLynx-ing? While developing T-Tris, I did download the game to up to 4 Lynx in paralell w/o problem.

 

Regarding the diode: I found the hint in another forum. I tried an resistor but it did not work. Too bad, I cannot remenber the explaination ...

Share this post


Link to post
Share on other sites

the inactive state is 5V. When some other lynx sends a 0 we don't want our Lynx 5V to block the communication. A diode works as an AND gate.

Share this post


Link to post
Share on other sites

the inactive state is 5V. When some other lynx sends a 0 we don't want our Lynx 5V to block the communication. A diode works as an AND gate.

Share this post


Link to post
Share on other sites

Reminder to myself: don't post to newsgroups while riding in an underground train in Hamburg... You just get double postings

Share this post


Link to post
Share on other sites

the inactive state is 5V. When some other lynx sends a 0 we don't want our Lynx 5V to block the communication. A diode works as an AND gate.

 

Just to check if I understand: The inactive state of the TX port is 5V. If connected directly with the RX/TX line, the Lynx cannot sink enough current to pull the line below the 0-level (IIRC < 1.5V).

So the diode will prevent current from the TX to the RX/TX line. So a sufficiently high resistor might also work.

Am I right?

  • Like 1

Share this post


Link to post
Share on other sites

Reminder to myself: don't post to newsgroups while riding in an underground train in Hamburg... You just get double postings

 

:-)

Share this post


Link to post
Share on other sites

 

You mean two Lynx'es w/o ComLynx-ing? While developing T-Tris, I did download the game to up to 4 Lynx in paralell w/o problem.

 

Regarding the diode: I found the hint in another forum. I tried an resistor but it did not work. Too bad, I cannot remenber the explaination ...

Not so much for the uploading.

 

PS: parallel upload to several lynxes never worked reliable for me.

Share this post


Link to post
Share on other sites

ComLynx is open collector circuit. You can connect many Lynxes in parallell. If you use resistors then every Lynx will source some current. The talking Lynx may not be able to sink the amount. Using a diode blocks the current flowing from inactive 5V to active 0.

Share this post


Link to post
Share on other sites

I have to rework all the old hardware shit I think.

JUst queues nicely intoshacky power connector, shacky comlinx connectors, shacky cartridge connector ... the whole stuff is falling apart...

Share this post


Link to post
Share on other sites

*rotfl*

 

bs42: the interface you sold me a zillion years ago uses a resistor between RX and TX ;-)))) Time to change that

Share this post


Link to post
Share on other sites

sage, the difference is that the CP2022 solution is powered by the USB. The MAX232 solution is powered by the Lynx and I doubt that the 5V does provide 500mA as the USB can.

The Lynx simply can't pull down the 5V from the CP2022.

It wasn't like it did not work at all but the received values were corrupted.

Edited by 42bs

Share this post


Link to post
Share on other sites

hm. valid point. but it might be the source of the problem if I have multiple lynxes at one adapter (parallel upload, comlynx debugging).

 

the diode modification worded very well with my new usb adapters with 31250/62500baud.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...

  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...