HP-48 and Win8

[cyrille de brébisson]

Hello,

As stated earlier, the USB<->serial converter is the key.

I once had a heated argument with one of the HP engineers working on high end workstation regarding having build in, native RS232 on modern computers (he was against, saying that we could use RS232<->USB converters and that he did not want to put these old tech on his shiny new computer (I mean he was designing it))...

The problem is that RS232 at 115200 baud can send 1 byte in 1/10h of a millisecond and wait for an immediate reply. XModem, for example has a 128 bytes packet with a 1 byte ack.
This means that a packet takes 10ms to send and then 1/10th of a millisecond to ack.

USB has a 1 millisecond 'heartbeat' and a 1K packet size (send ever 1 ms). so, most USB <-> serial converters drivers will wait for a full 1KB to send or a couple of milliseconds before sending data to the converter.

The net result is that communication speed drops drastically because the 3 protocols (XModem, USB and driver to convertor) gets in each-others way.

Ergo, you need a convertor that will send data as soon as available and not wait. Not all convertors will do that.

Cyrille