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IS80C31-40W Datasheet(PDF) 8 Page - Integrated Silicon Solution, Inc |
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IS80C31-40W Datasheet(HTML) 8 Page - Integrated Silicon Solution, Inc |
8 / 43 page IS80C51 IS80C31 8 Integrated Silicon Solution, Inc. — 1-800-379-4774 MC003-1D 11/19/98 ISSI® SPECIAL FUNCTION REGISTERS The Special Function Registers (SFR's) are located in upper 128 Bytes direct addressing area. The SFR Memory Map in Figure 6 shows that. Not all of the addresses are occupied. Unoccupied addresses are not implemented on the chip. Read accesses to these addresses in general return random data, and write accesses have no effect. User software should not write 1s to these unimplemented locations, since they may be used in future microcontrollers to invoke new features. In that case, the reset or inactive values of the new bits will always be 0, and their active values will be 1. The functions of the SFRs are outlined in the following sections, and detailed in Table 2. Accumulator (ACC) ACC is the Accumulator register. The mnemonics for Accumulator-specific instructions, however, refer to the Accumulator simply as A. B Register (B) The B register is used during multiply and divide operations. For other instructions it can be treated as another scratch pad register. Program Status Word (PSW). The PSW register contains program status information. Figure 6. Internal Data Memory and SFR Memory Map Accessible by Direct Addressing Not Available in IS80C51/31 Accessible by Direct and Indirect Addressing 80H 7FH 0 FFH 80H Upper 128 Lower 128 Special Function Registers Ports, Status and Control Bits, Timer, Registers, Stack Pointer, Accumulator (Etc.) B ACC PSW IP P3 IE P2 SCON P1 TCON P0 Bit Addressable F8 F0 E8 E0 D8 D0 C8 C0 B8 B0 A8 A0 98 90 88 80 FF F7 EF E7 DF D7 CF C7 BF B7 AF A7 9F 97 8F 87 SBUF TMOD SP TL0 DPL TL1 DPH TH0 TH1 PCON Figure 7. Lower 128 Bytes of Internal RAM 78 70 68 60 58 50 48 40 38 30 28 20 18 10 08 00 7F 77 6F 67 5F 57 4F 47 3F 37 2F 27 1F 17 0F 07 ...7F 0 ... BANK3 BANK2 BANK 1 BANK 0 8 BYTES REGISTER BANKS BIT ADDRESSABLE SEGMENT SCRATCH PAD AREA |
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