Howto add serial port to WL-500gx/gp

[sodb]

I have a 500gx running 1.9.2.7-5a. Before opening the case and possible break warranty I wanted to check how the internal serials are controlled.
I see the following:

[admin@wl500gx root]$ more /proc/tty/driver/serial
serinfo:1.0 driver:5.05c revision:2001-07-08
0: uart:16550A port:B8000300 irq:3 baud:115740 tx:630 rx:0 RTS|DTR
1: uart:16550A port:B8000400 irq:0 tx:0 rx:0 CTS|DSR|CD

That shows that two ports are available. Usually (in other Linux systsems) the serials devices have names /dev/ttyS0 and /dev/ttyS1. In de asus I only see /dev/tts/0 and /dev/tts/1.
trying to set baud rate using busybox stty applet results in the following:

[admin@wl500gx harddisk]$ ./busybox stty 9600 < /dev/tts/0
[admin@wl500gx harddisk]$ more /proc/tty/driver/serial
serinfo:1.0 driver:5.05c revision:2001-07-08
0: uart:16550A port:B8000300 irq:3 baud:9615 tx:630 rx:0 RTS|DTR
1: uart:16550A port:B8000400 irq:0 tx:0 rx:0 CTS|DSR|CD

It seems that the baud rate is only approximately set on the device. Probably accurate enough. Echoing some characters shows:

before
0: uart:16550A port:B8000300 irq:3 baud:9615 tx:630 rx:0 RTS|DTR
after echo "1234567890" > /dev/tts/0 it reads:
0: uart:16550A port:B8000300 irq:3 baud:9615 tx:642 rx:0 RTS|DTR

showing that the charaters are being transmitted.

Stty changes can also be made to second port; however, echoing to the second port /dev/tts/1 results in a full hang-up of the system. Need to power cycle.

Does anyone has experimence with sending/receiving messages through both the serials from the shell (thus not as default serial terminal at boot-up as is shown earlier in this thread)?

Another question is about the logical levels of this interface. Is it based on 3.3V or normal TTL 5V signals? In other words, can I connect a normal MAX232 for the signal conversion between RS-232 and the uart ports of the WL500G?