Johnson signed after visiting with the Cowboys and taking a physical.

"For a lot of reasons, he really just felt the Cowboys were the right fit," said Johnson's agent, Jerrold Colton. "He's so thankful to them for giving him this opportunity. He is very determined to prove they made a wise decision in believing in him."

Johnson, who played the last three seasons for the Chicago Bears, can't play until the second half of the season because of an eight-game NFL suspension for violating probation on a gun charge. But he could provide late-season depth on a defensive line that lost starting nose tackle Jason Ferguson for the year because of a tore right biceps in the opener.

The Bears released Johnson on June 25, three days after he was pulled over by police in Arizona. He already had served a two-month jail term for the gun charge and been suspended by the NFL for violating the league's personal conduct policy.

Police in Gilbert, Ariz., closed the June case without charging Johnson, who was stopped for speeding. His blood alcohol level was under the presumptive limit for DUI in Arizona, when he was stopped.