ES:DI, but does not store the result. The length of the string, in BCD

digits, is specified in CL. Unlike Intel string operations CL, DI & SI are
unchanged by the operation. The Zero Flag (ZF) is set if the result is zero.
The Carry Flag (CF) and Overflow Flag (OF) appear to be set by the
subtraction of the most significant digits.

Note that 0F is treated as <POP CS> on the 88/86 and prefixes newer
instructions on 286+ CPUs.

(Supplied by Anthony Naggs)