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AT89LS53-12JC Datasheet(PDF) 9 Page - ATMEL Corporation |
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AT89LS53-12JC Datasheet(HTML) 9 Page - ATMEL Corporation |
9 / 35 page 9 AT89LS53 0851C–MICRO–3/06 Data Memory - RAM The AT89LS53 implements 256 bytes of RAM. The upper 128 bytes of RAM occupy a parallel space to the Special Function Registers. That means the upper 128 bytes have the same addresses as the SFR space but are physically separate from SFR space. When an instruction accesses an internal location above address 7FH, the address mode used in the instruction specifies whether the CPU accesses the upper 128 bytes of RAM or the SFR space. Instructions that use direct addressing access SFR space. For example, the following direct addressing instruction accesses the SFR at location 0A0H (which is P2). MOV 0A0H, #data Instructions that use indirect addressing access the upper 128 bytes of RAM. For example, the following indirect addressing instruction, where R0 contains 0A0H, accesses the data byte at address 0A0H, rather than P2 (whose address is 0A0H). MOV @R0, #data Note that stack operations are examples of indirect addressing, so the upper 128 bytes of data RAM are avail- able as stack space. Programmable Watchdog Timer The programmable Watchdog Timer (WDT) operates from an independent oscillator. The prescaler bits, PS0, PS1 and PS2 in SFR WCON are used to set the period of the Watchdog Timer from 16 ms to 2048 ms. The available timer periods are shown in the following table and the actual timer periods (at VCC = 5V) are within ±30% of the nominal. The WDT is disabled by Power-on Reset and during Power Down. It is enabled by setting the WDTEN bit in SFR WCON (address = 96H). The WDT is reset by setting the WDTRST bit in WCON. When the WDT times out without being reset or disabled, an internal RST pulse is generated to reset the CPU. Table 7. Watchdog Timer Period Selection WDT Prescaler Bits Period (nominal) PS2 PS1 PS0 0 0 0 16 ms 0 0 1 32 ms 0 1 0 64 ms 0 1 1 128 ms 1 0 0 256 ms 1 0 1 512 ms 1 1 0 1024 ms 1 1 1 2048 ms Table 6. SPDR—SPI Data Register SPDR Address = 86H Reset Value = unchanged SPD7 SPD6 SPD5 SPD4 SPD3 SPD2 SPD1 SPD0 Bit 76543210 |
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