W8SDZ@SIMTEL20.ARPA (Keith Petersen) (08/15/87)
>I just got them working. The key is to make _sure_ the modem is set >to 'quiet' mode - no result codes or things like 'RING', CONNECTED', >etc. The VAX will immediately drop the line if it sees anything coming >from a modem without DCD, DSR, and CTS on. > >Incidentally, in testing, I was mildly surprised to note that XMODEM >file transfer at 9600 baud (ARQ) was only about 50% faster than at >2400 baud. This was done on a 4Mhz Z80 with 8" drives. Also, terminal >I/O using XMODEM (or a very simple dumb terminal emulator written in >assembler using BIOS calls) drops characters at 9600, but not at 2400. >It may not be fast enough to handle two 9600 baud ports at the same >time (terminal and modem). The key to greater thruput with the USR HST 9600 is to run the modem<-->computer interface at 19200. This allows the computer to fill the MNP packet buffer faster after each MNP packet is sent. Thruputs should be in excess of 10,000 bps that way. This works on a PC-clone I'm using. If you set up your VAX for 19200 on the interface you'll notice a improvement in downloads and terminal sessions. I use MEX114 on my CP/M machine with an old Soroc 120 terminal. The modem and console ports are standard polled I/O devices (no interrupts) and have no problems with dropped characters. Your problems with dropped characters is probably your terminal. Try a file transfer using MEX114 on the CP/M machine, with the "Q" (quiet) option during receive. I have been successful in using 19200 on the CP/M machine to send to the modem for file transfers. It's no good for terminal sessions because my Soroc 120 terminal can't keep up with the console I/O at 19200. --Keith Petersen Arpa: W8SDZ@SIMTEL20.ARPA Uucp: {bellcore,decwrl,harvard,lll-crg,ucbvax,uw-beaver}!simtel20.arpa!w8sdz GEnie: W8SDZ RCP/M Royal Oak: 313-759-6569 - 300, 1200, 2400 (V.22bis) or 9600 (USR HST)