>I figured somebody with a lot more knowledge then I have would have >answered by now too. The answer to "how is flow control handled >on the HP3000" is that it depends on the term type used (set either >in sysgen or in the HELLO command). > >For there standard terminals (using term type 10) the HP3000 uses a >very non-standard protocol called ENQ-ACK. I forget the details but >someone else can enlighten you if more information is need or I can >dig up some old documentation. > >NMD > > I'm not sure what flow control or other information you need regarding the Classic HP 3000's, so pardon me if I ramble. I'm sure Ross et al at Telamon can provide more details, but if I remember, the the standard MPE V/E TT10 file uses Enq-Ack as a pacing method rather than as true flow control. The HP would send a buffer (typically 80 bytes, but in the old days it was configurable) followed by an ENQ character. The terminal would absorb the characters and respond with an ACK character. The HP would then send the next block, etc. But, there was also a time-out, which if I remember correctly was also configurable and was something like 10 seconds. If the HP 3000 didn't receive an ACK within 10 seconds it would proceed as if it had and would sent the next buffer of output data. The early terminals (HP 2600) could run at very high data rates - as high as 2400, but they had trouble keeping up with the data at such high transmission rates and ENQ-ACK was the way they kept the system from overrunning the terminal. The older HP 3000's didn't always respond to X-OFF - either the first time an X-OFF was sent or sometimes the first dozen or so X-OFFs. Some HP devices (like the old serial printers) had a "robust X-OFF" feature which meant that if after the first X-OFF they were still receiving data, they would keep sending X-OFFs until the HP 3000 stopped sending data. Some datacomm devices REALLY appreciated robust X-OFF (muxs, modems) and caused all sorts of problems. ESC was another problem character. It was paired with ":" and ";" so that the user could easily turn input echo on or off. Unfortunately, the processing of the ESC in the input data stream took some time and caused those with smaller (slower) systems no end of grief at data rates of 9600 or 19200. The Micro GX, XE, and Series 37 suffered this problem. Programs like PSCREEN, (and many others) which read data from terminal memory would have their FREADs fail with data overruns if there were ESC sequences in them. The ESC sequences took so long to check to make sure they were not ESC ; or ESC : that a buffer overrun would occur (if anyone has this problem and needs the workaround, let me know and I'll dig up the solution). Also, the flow control options vary with the release of MPE V/E. On 2P and older versions you could change the size of the Enq-Ack buffer from 80 bytes to as much as 255 bytes. "Progressing" to 3P took this "feature" away. Anyway, there were a lot of quirks and some really nice features as well. Hope this helps. -------------------------------------------------------------- John Korb email: [log in to unmask] Innovative Software Solutions, Inc. The thoughts, comments, and opinions expressed herein are mine and do not reflect those of my employer(s), or anyone else.