I'm currently working on a small project to permanently attach a Raspberry Pi to my IIci over the RS-422 serial ports. So far I got everything working except for hardware flow control. The RS-232 USB adapter I'm using is definitely capable of using it when connecting to a similarly vintage Unisys terminal over RS-232.
When I checked using both the modem and printer ports HSO (pin 1) signal level, it seems to be pulling down from 0v to -100mv when comparing with ground (pin 4), which I think is much too low for the adapter to recognise. In the other direction I also get no change when testing with zterm and RTS pulled down (connected to HSI, pin 2 on the mac). With nothing connected HSI is pulled high to 5v on the mac.
My first question is if this is normal and I need to make a circuit to convert to these voltage levels, or if I'm just doing something wrong, or possibly if the driver chip in the mac is faulty. I've gone over the datasheet for the driver but couldn't quite work out what kind of signal to expect on those lines.
And my question is if there is an easier method I can use to control and monitor the HSI / HSO pins more directly from the Mac? Right now I'm using zterm and just blast a text file across and wait for HSO to assert. (Testing with XON/XOFF shows regular throttling and without the text file arrives with large chunks missing, confirming that HSO should have asserted when hardware handshake is enabled.)
When I checked using both the modem and printer ports HSO (pin 1) signal level, it seems to be pulling down from 0v to -100mv when comparing with ground (pin 4), which I think is much too low for the adapter to recognise. In the other direction I also get no change when testing with zterm and RTS pulled down (connected to HSI, pin 2 on the mac). With nothing connected HSI is pulled high to 5v on the mac.
My first question is if this is normal and I need to make a circuit to convert to these voltage levels, or if I'm just doing something wrong, or possibly if the driver chip in the mac is faulty. I've gone over the datasheet for the driver but couldn't quite work out what kind of signal to expect on those lines.
And my question is if there is an easier method I can use to control and monitor the HSI / HSO pins more directly from the Mac? Right now I'm using zterm and just blast a text file across and wait for HSO to assert. (Testing with XON/XOFF shows regular throttling and without the text file arrives with large chunks missing, confirming that HSO should have asserted when hardware handshake is enabled.)
