Toshiba TLCS-90 Series Data Book page 209

TOSHIBA TMP90C840
o Parity/Overflow flag (P/V)
This flag has two funct ions. One is to indicate the parity (p)
resulted from a logical opepration (AND, OR, or XOR). It is set to
"I"
when the result is even, and "0" for odd parity.
The other is to indicates the overflow (V) in an arithmetic operation
(ADD, ADC, SUB, SBC, or CP). The flag is set to
"I"
when the result
cannot be expressed by a signed integral number.
The P/V flag selects either function according to the instruction.
o Carry. flag (C)
The flag is set to
"I"
if a carry or borrow has occurred on the MSB of
the ALU.
o Expansion carry flag (X)
Like the carry flag (C),
it is set to "I" when the MSB of the ALU
involves a carry or borrow as a result of an operation except that it
applies to a wider range of instructions (e.g., INC rr).
o Half carry flag (H)
It is set to "1" when a carry or borrow has occurred on the 4th bit of
the lower side in the ALU.
o Addition/Subtraction flag (N)
This flag is set to "I" if the executed operation is
a
subtraction
(SUB, SBC, CP, or DEC).
o Interrupt enable flag (IFF)
A maskab Ie interrupt is enab led or disab led by this flag. This flag
is set to
"I"
by an EI instruction and "0" by an DI instruction.
(Note) This flag is shared with the alternative register
F'.
(3) Registers B, C, D, E, Hand L
All these registers have an 8-bit configuration. They function as
16-bit register pairs (concatenated BC, DE and HL) as well as
independent 8-bit register. Registers B or register pair BC is also
used as a counter for the loop instruction (DJNZ). Register pair HL
is used for 16-bit data processing including l6-bit arithmetic/logic
operations.
(4) Registers A',
F',
B', C', D', E', H' and L'
These registers have the same structure as the main registers (A,
F,
B, C, D, E, Hand L). They are called alternat ive registers. There
is no instruction that directly accesses these alternative registers,
but its data can be processed by a register exchange instruction.
Following are examples of register· exchange insturctions that allow
the exchange of data between a main register and an alternative
register:
EX AF,AF'
EXX
(5) Registers IX, IY, BX and BY
IX and IY are 16-bit independent registers called index registers. BX
and BY are 4-bit independent registers and referred to as bank
registers.
These registers are used mainly for specifying memory addresses, and
generate 20- bit addresses. IX and IY registers are also used for
16-bit additions.
MPU90-11