On Tue, Feb 27, 2018 at 6:24 PM, Brian White <[email protected]> wrote:
> Yes, except most generic level shifters (like that sparkfun one) don't > have enough channels to do all the flow control lines, so you might get > rts/cts but not dtr/dts. > AFAIK RTS/CTS is irrelevant when using TPDD other than that CTS must not be found deasserted. That can be handled via loopback. Or not! If it needs the RTS/CTS line to power level conversion, maybe it has to pass through. DTR/DTS is obeyed by TS-DOS and may be used by the drive. It's used as a cable detect, at least. Don't know what lines or how they are used to do the level conversions. I did hunt up some special ones that do have enough channels, but I haven't > tried to actually make an adapter out of it yet. For one thing it needs a > power source which might not be doable just from parasitizing the serial > port itself. > > That is what we think happens... a PC serial port generally provides 12v . A Model 100 provides 5V signals which is marginal for RS232 but in-spec. The TPDD is at TTL levels so the presumed circuitry does the conversion. > The original real cable and the Marty Goodman one does not require a power > source, because it does not bother to do full proper level shifting, it > just relies on a trick which happens to work on a M100. > I don't know about that. As long as it adapts TTL level signals to RS232 at at least 5V, it's doing its job and is in-spec. Also of interest is that I've never had any problem with real TPDD cables when connected to a PC instead of a Model T. In other words, TPDD cables don't just work with the Model Ts. So any good replacement design should work as well. > In the end, the diode cable ends up looking most practical after all > because it sidesteps the whole issue of a power source. > Agree. -- John.
