RCL and RCR perform a 9-bit, 17-bit or 33-bit bitwise
rotation operation, involving the given source/destination (first)
operand and the carry bit. Thus, for example, in the operation
RCL AL,1, a 9-bit rotation is performed in which AL is
shifted left by 1, the top bit of AL moves into the carry flag,
and the original value of the carry flag is placed in the low bit of
AL.
The number of bits to rotate by is given by the second operand. Only the bottom five bits of the rotation count are considered by processors above the 8086.
You can force the longer (286 and upwards, beginning with a C1
byte) form of RCL foo,1 by using a BYTE prefix: \c{RCL
foo,BYTE 1}. Similarly with RCR.