Linksys WRT54GR v1.0

Overview
OEM Gemtek WRTR-136C (WRTR-136C_V02)

WRT54GR v1.x serial numbers appear to start with MK9.

Links of Interest

 * On the OpenWrt Forums

Serial Pinouts
CON1 (GND) (RxD) (GND) (VCC) (VCC) [TxD]

Pictures
User Images