Specifications

Processor Description (V40)
number of bits set. This flag is useful for checking the parity of
ASCII characters.
AC [AF] (Auxiliary Flag) - AC [AF] is set if an addition results
in a carry from the four least significant bits of the result. This is
true for both byte and word addition. This flag is used by the
CPU for BCD arithmetic operations.
Z [ZF] (Zero Flag) - Z [ZF] is set if the result of an arithmetic or
logical operation is zero. A common use of this flag is to
determine if two numbers are equal. The program subtracts the
two values and if Z [ZF] is set, the values are equal.
S [SF] (Sign Flag) - Arithmetic and logic operations set S [SF]
equal to the high order bit of the result. This is bit 7 for byte
operations and bit 15 for word operations. For signed binary
operations, S [SF] is reset for positive results and set for negative
results. Programs using unsigned operations usually ignore S [SF]
because the high order bit does not reflect the sign of the result.
V [OF] (Overflow Flag) - The V [OF] flag is set if the result of
an operation is too large a positive number or too small a negative
number to fit into the destination. The application program can
use the overflow flag to determine if the result of two’s
complement arithmetic operation is out of range.
Control Flags
MD (Mode Flag) - The CPU operates in either native or
emulation mode. In native mode, the CPU executes the standard
8086/186 instructions in addition to instructions unique to the
V40. In emulation mode, the CPU executes an 8080 based
instruction set. The MD flag is used to distinguish between the
two modes. MD is programmed using specific instructions to put
the CPU in the native mode (MD is set) or emulation mode (MD
is reset). Refer to page 5-33 for more information.
DIR [DF] (Direction Flag) - The CPU supports string operations
to manipulate linear arrays of data organized as words, bytes,
nibbles, or bits. Index registers are used to point to elements of
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