TMP47P201 datasheet(11/32 Pages) TOSHIBA

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TOSHIBA CORPORATION

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TMP47C101/201

(2)

Zero detect information (Z)

This information is “1” when the operation result or the

data to be transferred to the accumulator/data mem-

ory is “0000B”.

Figure 2-11. ALU

Example:

The carry information and zero detect

information for 4-bit additions and subtrac-

tions.

Operation

Result

4 + 2 =

7 + 9 =

9 + 9 =

Operation

Result

8 - 1 =

2 - 2 =

5 - 8 =

3 (1101B)0

2.5.2 Accumulator (Acc)

The accumulator is a 4-bit register used to hold source data or

results of the operations and data manipulations.

Figure 2-12. Accumulator

Figure 2-13. Flags

2.6 Flags

There is a carry ﬂag (CF), a zero ﬂag (ZF), a status ﬂag (SF), and

a general ﬂag (GF), each consisting of 1 bit. These ﬂags are set

or cleared according to the condition speciﬁed by an instruc-

tion. When an interrupt is accepted, the ﬂags are saved on the

stack along with the program counter. When the [RETI]

instruction is executed, the ﬂags are restored from the stack to

the states set before interrupt acceptance.

(1)

Carry ﬂag (CF)

The carry ﬂag holds the carry information received from

the ALU at the execution of an addition/subtraction

with carry instruction, a compare instruction, or a

rotate instruction. With a carry ﬂag test instruction, the

CF holds the value speciﬁed by it.

Addition/subtraction with carry instructions [ADDC A,

@HL], [SUBRC A, @HL]

The CF becomes the input (Cin) to the ALU to hold the

carry information.

Compare instructions [CMPR A, @HL], [CMPR A, #k]

The CF holds the carry information (non-borrow).

Rotate instructions [ROLC A], [RORC A]

The CF is shifted into the accumulator to hold the car-

ry information (the data shifted out from the accumu-

lator).

Carry flag test instructions [TESTP CF], [TEST CF]

With [TESTP CF] instruction, the content of the CF is

transferred to the SF then the CF is set to “1”.

With [TEST CF] instruction, the value obtained by in-

verting the content of the CF is transferred to the SF

then the CF is cleared to “0”.

(2)

Zero ﬂag (ZF)

The zero ﬂag holds the zero detect information (Z)

received from the ALU at the execution of an opera-

tional instruction, a rotate instruction, an input instruc-

tion, or a transfer-to-accumulator instruction.

(3)

Status ﬂag (SF)

The status ﬂag provides the branch condition for a

branch instruction. Branch is performed when this ﬂag

is set to “1”. Normally the SF is set to “1”, so that any

branch instruction can be regarded as an uncondi-

tional branch instruction. When a branch instruction is

executed upon set or clear of the SF according to the

condition speciﬁed by an instruction, this instruction

becomes a conditional branch instruction. During

reset, the SF is initialized to “1”, other ﬂags are not

affected.

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