RCL shifts the bits of the destination operand to the left by the number of bit positions specified in the count operand. A bit shifted out of the left (high-order) end of the destination enters the carry flag (CF), and the displaced carry flag rotates around to enter the vacated right-most bit position of the destination. Another way of looking at this is to consider the carry flag as the highest order bit of the word being rotated.
The shift is repeated the number of times indicated by the second operand, which is either an immediate 8-bit value (max. 1 on the 8086 processor) or the contents of the CL register. To reduce the maximum execution time, the 80186+ uses only the lower 5 bits of the count, limiting the count value to 31; the 8086 uses all 8 bits of count.
If the count operand is not an immediate 1, the overflow flag (OF) is undefined; otherwise RCL sets OF to 0 if destination's sign bit was not changed by the operation, to 1 if the sign bit was changed.