On Sat, Dec 1, 2018 at 5:04 PM Jerry Stratton <model...@hoboes.com> wrote: > > Would these be only for connecting to an actual TPDD hard drive, or would > they be useful for connecting to the serial port of, say, a Raspberry Pi?
I don't think they can be reliably used for anything other than connecting an M100-family machine to a TPDD. > Is special hardware needed for using TPDD directly to another computer’s > serial port? That is, other than DB-25 RS232 on the Model 100 end to the > serial port on the other computer? Well... that depends. In RS232-C communications, there's "the spec" and then there's "everything actually implemented out in the world". The spec (https://en.wikipedia.org/wiki/RS-232#Voltage_levels) says that there are two voltage level ranges: +3 to +15 and -3 to -15. The higher voltage is a 0 and the lower a 1. However, UARTs typically output 5v for 1 and 0v for 0; this is known as TTL-level serial. To convert TTL to RS232c you need a line driver. And LOTS of actual serial port line driver implementations don't follow the spec in one way or another: Some require higher peak-to-peak deviation than the spec says; some don't implement the negative voltages properly (1 is clamped to 0 volts); etc. For whatever reason, the TPDD serial port is TTL level, and the line driver is located in the serial cable. The TPDD board I'm referencing (yes - it's that one) > (Assuming this is the PCB you’re talking about: > https://oshpark.com/profiles/Rick_Shear) implements a line driver with just a few transistors to basically mimic (I think) the real TPDD cable. However, the signals from this cable (on the DB25 end) are not true RS232 and are only really expected to work with the line driver in the M100. Now, you may get lucky and it works to connect your PC to a TPDD for use with tpddtool, etc. But, there are neve any guarantees with serial line drivers that are out of spec. As far as connecting a 100-series machine to some other device, you need that device to implement RS232c. As John says, there's a Pi Hat for RS232c from a RPi board. I can't really guess whether or not this TPDD cable would correctly talk to the TTL serial port on an RPi. -Josh
