Using IBIC (DOS Interactive Control) to talk to HP3457a DVM?

I am trying to determine the maximum data output speed of an existing setup;

NI   AT-GPIB/TNT   ISA card in a Pentium 500 DOS computer

HPIB cable to HP 3457a DVM

IBdiag and IB test say my card is working ok.

I can use  IBIC to get some communication with the DVM (IBRD 16 reports the current voltage)

but  if I try to send a command to the DVM such as IBWRT "BEEP"  or DISPLAY OFF , nothing happens.

I suspect I may have the EOI flag or EOS flag or ??? set wrong    (EIO last  now = 1,  EOS now = 0).

How can I send commands to the HP3457a?  and ideas appreciated!

Thanks!