Both are Gig ports so second can be used in connecting a PC or some other device like STB however a word of caution and remember not to connect a device which will further service lots of devices. All the traffic need to go through and processed by AP and this may impact the overall performance. Take a look at its datasheet
i just tested one of My R700. its works. Here is my topology for your info:
ZD with DHCP server enabled (192.168.0.2) ------- POE injector ----------- R700 with dynamic Ip ---- Win 7 based Dell Laptop. i got auto IP. no problem
when you connect your computer or laptop to second ethernet port, do you get link status UP on the laptop or not AP??