Downgrades ding AMD shares

Advanced Micro Devices shares fell 1 13/16, or 6 percent, to 28 11/16 Wednesday after a pair of brokerage firms downgraded the chipmaker.

Prudential Securities cut AMD from a "strong buy" rating to "accumulate" while Banc of America Securities slashed it from a "strong buy" recommendation to a "market perform."

Banc of America analyst Rick Whittington also cut rival Intel (Nasdaq: INTC) to a "market perform" rating from a "strong buy."

Intel shares were off 3 3/8 to 61 9/16 while competitor Rambus (Nasdaq: RMBS) moved up 4 1/8 to 80 15/16.

AMD (NYSE: AMD) hit a 52-week high of 48 1/2 in June after falling to a low of 8 3/16 in October. It also split 2-for-1 in August.

AMD beat the Street in its second quarter, earning $207.1 million, or $1.21 a share, on sales of $1.17 billion.

First Call Corp. consensus expects it to earn 63 cents a share in the third quarter and $2.59 a share in the fiscal year.

Fourteen of the 17 analysts following the stock rate it either a "buy" or "strong buy."