I asked Vladimir in passing how he preferred to talk to things via the serial port, and he wrote this. It is now contained in /users/dmass/scripts/serial_test.tcl :

#!/usr/bin/env tclsh

global SERPORT
set SERPORT [open "/dev/ttyS0" "w+"]

fconfigure $SERPORT -mode 9600,n,8,1 -handshake none -buffering line

proc run_query { command } {
global SERPORT

puts $SERPORT "$command"
flush $SERPORT
gets $SERPORT line

return $line
}

#@puts [run_query "BEEP?"]

while { 1 } {

    puts "[clock format [clock seconds]]\t[run_query "TEC:T?"]"
    after 100
    }