Originally posted by Madaboutpix The operating manual labels it "Microphone/cable release terminal"
Also, if you can catch the light just right, you'll see that the rubber flap covering this port has a cable release icon and the letters 'MIC'. It sounds like you already have a wired shutter remote. Just FYI, I recently bought a JJC brand MA-PK1 on Amazon for about $8.50. The Pentax OEM unit CS-310 was $50. Like I said in another post, I'm a loyal Pentaxian but that was too big a price difference. So far the JJC works just fine.