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P89C51UFAA Datasheet(PDF) 19 Page - NXP Semiconductors |
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P89C51UFAA Datasheet(HTML) 19 Page - NXP Semiconductors |
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19 / 32 page  Philips Semiconductors Product specification 89C51/89C52/89C54/89C58 80C51 8-bit microcontroller family 4K/8K/16K/32K Flash 1999 Oct 27 19 Reduced EMI Mode The AO bit (AUXR.0) in the AUXR register when set disables the ALE output. Reduced EMI Mode AUXR (8EH) 7 6 54 32 1 0 – – – – – – – AO AUXR.0 AO Turns off ALE output. Dual DPTR The dual DPTR structure (see Figure 13) is a way by which the chip will specify the address of an external data memory location. There are two 16-bit DPTR registers that address the external memory, and a single bit called DPS = AUXR1/bit0 that allows the program code to switch between them. • New Register Name: AUXR1# • SFR Address: A2H • Reset Value: xxxx00x0B AUXR1 (A2H) 76 54 32 10 – – – – GF2 0 – DPS Where: DPS = AUXR1/bit0 = Switches between DPTR0 and DPTR1. Select Reg DPS DPTR0 0 DPTR1 1 The DPS bit status should be saved by software when switching between DPTR0 and DPTR1. The GF0 bit is a general purpose user-defined flag. Note that bit 2 is not writable and is always read as a zero. This allows the DPS bit to be quickly toggled simply by executing an INC AUXR1 instruction without affecting the GF2 bit. DPS DPTR1 DPTR0 DPH (83H) DPL (82H) EXTERNAL DATA MEMORY SU00745A BIT0 AUXR1 Figure 13. DPTR Instructions The instructions that refer to DPTR refer to the data pointer that is currently selected using the AUXR1/bit 0 register. The six instructions that use the DPTR are as follows: INC DPTR Increments the data pointer by 1 MOV DPTR, #data16 Loads the DPTR with a 16-bit constant MOV A, @ A+DPTR Move code byte relative to DPTR to ACC MOVX A, @ DPTR Move external RAM (16-bit address) to ACC MOVX @ DPTR , A Move ACC to external RAM (16-bit address) JMP @ A + DPTR Jump indirect relative to DPTR The data pointer can be accessed on a byte-by-byte basis by specifying the low or high byte in an instruction which accesses the SFRs. See application note AN458 for more details. |
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