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TMP47C101M Datasheet(PDF) 11 Page - Toshiba Semiconductor |
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TMP47C101M Datasheet(HTML) 11 Page - Toshiba Semiconductor |
11 / 32 page TOSHIBA CORPORATION 11/32 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 C Z 4 + 2 = 6 0 0 7 + 9 = 0 1 1 9 + 9 = 2 1 0 Operation Result C Z 8 - 1 = 7 1 0 2 - 2 = 0 1 1 5 - 8 = 3 (1101B)0 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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