[net.micro.cpm] TAC usage

LIN@mit-xx.ARPA (09/25/86)

a few months ago, I asked the list for a guide to doing XMODEM
transfers through a TAC from a TOPS-20 machine (the one at MIT-XX)
using MODEM.  The one concrete suggestion I got was to say SNQ instead
of S to do the download.  It didn't work.

I have no trouble downloading using MODEM on TOPS-20 to download when
I talk directly on a dial-up line to the TOPS-20 machine.

My problem is that when I attempt to download through the TAC, I get
the message "bad header in record 1", "bad header in record 2", etc
until my MODM700 program quits on me.

Any suggestions?

Thanks.  

Herb

mbarker@bbnccv.ARPA (Mike Barker) (09/26/86)

sounds like the TAC is in 7-bit ASCII mode, rather than binary.  Have
you tried B I S and B O S (I think those are the commands)?  They should
cause the TAC to go into binary mode with eight-bit characters (the
complemented count in the header is 8-bits, even if everything else is
only 7 bits).

    Good luck
    mike

WANCHO@SIMTEL20.ARPA (09/26/86)

Both MODEM and the newer TMODEM have code for two methods of
negotiating network binary mode for the TAC user for the duration of
the file transfer on TOPS-20 systems.  One method assumes that the
monitor does not double the IAC character (FFH) and thus allows the
user program to send the appropriate sequences in-band to the TAC.
The other method assumes that the monitor always doubles the IAC
character and provides a particular monitor call to provide the
capability to do that negotiation.

The problem is that some monitors double the IAC character always, but
have no local mod to provide the capability to turn on network binary
mode.  Thus, as Mike says, the user must give the TAC commands:

@B O S
@B I S

in that order.  The side effect of the @B I S is that the user can no
longer give any more TAC commands for the remainder of the session
with that host.  (When the host closes the connection after the user
logs out, the TAC port is set back to normal.)

The situation is further complicated in that neither the MODEM nor
TMODEM program{ have compilation conditionals to allow for this third
case where the monitor does the IAC doubling, but does not provide for
a monitor call.  The solution in those cases is to send this message
to your system wizard and have them contact me to work out a fix.

--Frank