Info about Z80 machine

Some machines had both sorts of port -- my Zenith Z90 has 3 serial ports , 2 of one flavour, one of the other. I can't remember which way round, but they are clearly labelled on the cxse. In theory a male connector should be used for a DTE, a female conenctor for a DCE. But don't bet on it. One of the worst 'serial sex offenders' (as I tend to call manufacturers who get this wrong) that I've come across was HP who routinely fitted DB25 sockets wired as DTEs. I find one of those little plug-to-socket adpaters with LEDs monitoring the important lines ot be very useful here If you plug it into an unknown port and connect nothing else to it, then at least one LED is likely to come on [1[ Be seeing which line(s) are driven you can make a good guess as to whether it's a DTE or DCE [1] OK, this fails if the serial port is powered from the handshake lines. Or if it expects to see an active line before powering up the output buffers. Such cases are rare but not unheard-of The other way is to find the RS232 buffers inside the device (for classic hardware these are likely to be separate ICs) and trace a few pins of the conencotr to them. If you find that pin 2 is connected to the output of a driver and pin 3 is conencted to the input of a receiver it's a good bet the prot is wired as DTE. As for the jumpers, the time I came acorss this was the HP82164 HPIL-RS232 interfce. There's a jumper plug you can fit either way round, one way gives DTE wiring, the other gives DCE -- in theory. Actually, it messes about with soem of the handshake lines, jumpering them together, etc. I have found the only sane thign to do is to set the jumper to DTE and leave it alone, Then wire up external adapters as needed. One of the few machiens to make this easy was the Tatung Einstein. It used a quincuncial 5 pin DIN plug, like the BBC micro, for the RS232 port. Unlike the Beeb, it was wired sensibly. If you plug it in upside odwn it swaps TxD with RxD and RTS with CTS. Just what you want. -tony