[GreenKeys] ASR33

[Chris Elmquist]

I am one of the classic computing guys here on this list...  although I
do not have any PDP-11 stuff currently, I have hooked the ASR33 to my
precious Altair680 and have not smoked it.

You need to make sure the ASR33 is wired for passive loop.  Do not
allow the '33 to source the loop current as it will do so at 130 to 160v
and whatever the serial interface is in the PDP, it might not be happy
with that.

So, you need to make sure the PDP is the source of the loop current and
the '33 is passive on both the xmit and the receive loops.

Personally, I would recommend using a 20mA to RS232 converter and then
connecting to the PDP with RS232.  This is more safe in many ways and
usually easier to achieve.

There were a number of sources for 20mA to RS232 converters discussed
on the list here, most going for $20 or less on eBay.

Do you know how to wire your PDP for RS232?

Chris

On Friday (09/18/2009 at 11:29PM -0500), Don Robert House wrote:
> You need to contact someone else who has already done what you are  
> attempting.
> I no longer have any of the Classic Computer guys in my email address  
> book.
> 
> I will copy a couple of men who might be able to steer you.
> 
> Guessing is not the best solution.  The smoke is hard to get back into  
> the unit.
> 
> Don
> K9TTY
> 
> 
> On 18 Sep 2009, at 6:49 PM, B M wrote:
> 
> Is the ASR33 capable of generating voltage/current spikes via the 20mA
> connection?  I realize the connection is passive, but what exactly is
> the 20mA connection driving? Should I be concerned about connecting
> the ASR33 directly to my old PDP-11's?  I am more concerned about
> ensuring the PDP-11 will be ok and not as concerned if something bad
> happens to the ASR33 since the TTY is much easier to fix/replace :-)
> 
> Is there any tests I could perform before hooking the TTY to my  
> computer?
> 
> Many thanks for any information.
> 
> --barrym
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-- 
Chris Elmquist