You can send the escape command (@K1) directly to your tnc: echo -e "\r\033@K1\r" > /dev/ttyS0
That'd be the right command for a DED hostmode TNC... most "user" TNCs it's "KISS ON\rRESTART\r" or similar. Will depend on the EPROM your TNC actually has. But once you have got it into KISS mode, typically the CON and STA leds will flash 3 times to acknowledge.
73 Gavin. --- Amateur radio station VK6HGR http://vk6hgr.ampr.org/ Email : grogers@vk6hgr.echidna.id.au Packet: vk6hgr@vk6hgr.#per.#wa.aus.oc