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ATMEGA640 Datasheet(PDF) 36 Page - Microchip Technology |
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ATMEGA640 Datasheet(HTML) 36 Page - Microchip Technology |
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36 / 436 page  36 ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET] DS40002211A The user should poll the EEPE bit before starting the read operation. If a write operation is in progress, it is neither possible to read the EEPROM, nor to change the EEAR Register. 9.3 General Purpose registers 9.3.1 GPIOR2 – General Purpose I/O Register 2 9.3.2 GPIOR1 – General Purpose I/O Register 1 9.3.3 GPIOR0 – General Purpose I/O Register 0 9.4 External Memory registers 9.4.1 XMCRA – External Memory Control Register A • Bit 7 – SRE: External SRAM/XMEM Enable Writing SRE to one enables the External Memory Interface.The pin functions AD7:0, A15:8, ALE, WR, and RD are activated as the alternate pin functions. The SRE bit overrides any pin direction settings in the respective data direction registers. Writing SRE to zero, disables the External Memory Interface and the normal pin and data direc- tion settings are used. • Bit 6:4 – SRL2:0: Wait-state Sector Limit It is possible to configure different wait-states for different External Memory addresses. The external memory address space can be divided in two sectors that have separate wait-state bits. The SRL2, SRL1, and SRL0 bits select the split of the sectors, see Table 9-2 on page 37 and Figure 9-1 on page 27. By default, the SRL2, SRL1, and SRL0 bits are set to zero and the entire external memory address space is treated as one sector. When the entire SRAM address space is configured as one sector, the wait-states are configured by the SRW11 and SRW10 bits. Bit 765 43210 0x2B (0x4B) MSB LSB GPIOR2 Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 000 00000 Bit 76543210 0x2A (0x4A) MSB LSB GPIOR1 Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 00000000 Bit 765 43210 0x1E (0x3E) MSB LSB GPIOR0 Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 000 00000 Bit 76543 210 “(0x74)” SRE SRL2 SRL1 SRL0 SRW11 SRW10 SRW01 SRW00 XMCRA Read/Write R/W R/W R/W R/W R/W R/W R/W R/W Initial Value 00000 000 |
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