Does anyone know the status of serial support on the powerbook 5xx series?

My powerbook has an internal modem and an external Printer/Modem
port.  From MacOS, the external port works just fine, but from NetBSD
serial port operations appear to hang the user process
initiating them.

If the external serial port is supported, is it named /dev/tty00,
/dev/tty01, or something else?  (I have no intention of using the internal
modem.)

What I really want to do is configure NetBSD on the powerbook to use a
serial console, but when I enable it from the booter, the machine hangs
just after transferring control to the kernel but before the kernel can
initialise the ite terminal.

The ports are both probed at boot time (when not attempting a serial
console):

zsc0 at obio0 chip type 0 
zsc0 channel 0: d_speed   9600 DCD clk 0 CTS clk 0
zstty0 at zsc0 channel 0
zsc0 channel 1: d_speed   9600 DCD clk 0 CTS clk 0
zstty1 at zsc0 channel 1

Any clues would be most welcome.
-- 
Tod McQuillin