On Tue, Dec 1, 2015 at 12:43 PM, Ethan Dicks <ethan.di...@gmail.com> wrote:
> On Tue, Dec 1, 2015 at 11:55 AM, Paul Koning <paulkon...@comcast.net> > wrote: > > I'm not sure I understand the question correctly. That article clearly > points out the 20 mA wires, and presumably that's where your ASR33 is > connected. The VT50 comes (according to the peripherals handbook) with a > standard 20 mA interface, optional RS232 interface. So it sounds like it > would be a matter of finding where the 20 mA connector on the VT50 is, and > plugging into that. > > > > Interestingly enough, the VT52 is listed as supporting either kind of > interface, but only one; "specify at time of order". > > I don't know that I've taken apart a VT50 or if there are internal > differences, but for the VT52, there's a ~2"x5" (from memory) PCB with > interface circuitry for either EIA or 20mA and a permanently-attached > cable with the appropriate connector on the host end. You take the > bottom of the terminal off, pop the board, pop the other one on and > it's switched. > > It would not be difficult to replicate either board, either by hand or > with a fabricated PCB. > > -ethan > Sorry about the wording of my question. Thanks for the replies. I was only able to get the VT50 to receive, I could not send. So I decided to research the problem. I found the link above, the author of the page says in effect 20mA did not work (for him) as desired. So I was wondering if anyone here has been successful to attach a M9970 to a VT50 or VT52. I spend more time on it, but I was curious if it was even worth it given the hardware. The author writes: -start quote-- I first tried to connect a PC with the 11/05 over a industrial RS232-to-20mA converter, but this failed. A 20mA interface works by one side providing a 20mA current, which drives receiver and transmitter of the closed loops for Transmit and Receive. But the 20mA interface of the PDP-11/05 is not a proper one: the receiver is more like a low impedance voltage sensor, while the transmitter simply switches voltage at the levels +3.5V to -15 V. At best you call the PDP-11/05 serial interface a "TTY interface": it is well suited to read data generated by mechanical switches to GND, and driving solenoids for transmit data. -end quote-- -- Bill
