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AT89LP428-20PU Datasheet(PDF) 11 Page - ATMEL Corporation |
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AT89LP428-20PU Datasheet(HTML) 11 Page - ATMEL Corporation |
11 / 149 page 11 3654A–MICRO–8/09 AT89LP428/828 3.3 External Data Memory AT89LP microcontrollers support a 16-bit external data memory address space. The external memory space is accessed with the MOVX instructions. The AT89LP428/828 does not support an external memory interface. However, some internal data memory resources are mapped into portions of the external address space as shown in Figure 3-3. These memory spaces may require configuration before the CPU can access them. The AT89LP428/828 includes 512 bytes of on-chip Extra RAM (EDATA) and 512/1024 bytes of nonvolatile Flash data memory (FDATA). Figure 3-3. External Data Memory Map 3.3.1 EDATA The Extra RAM is a portion of the external memory space implemented as an internal 512-byte auxiliary RAM. The Extra RAM is mapped into the EDATA space at the bottom of the external memory address space, from 0000H to 01FFH. MOVX instructions to this address range will access the internal Extra RAM. EDATA can be accessed with both 16-bit (MOVX @DPTR) and 8-bit (MOVX @Ri) addresses. When 8-bit addresses are used, the PAGE register (086H) sup- plies the upper address bits. The PAGE register breaks EDATA into two 256-byte pages. A page cannot be specified independently for MOVX @R0 and MOVX @R1. When 16-bit addresses are used (DPTR), the IAP bit (MEMCON.7) must be zero to access EDATA. MOVX instructions to EDATA require a minimum of 2 clock cycles. Extra RAM (EDATA) 0000 01FF 0200 03FF Flash Data (FDATA) Extra RAM (EDATA) 0000 01FF 0200 05FF Flash Data (FDATA) AT89LP428 AT89LP828 Table 3-3. PAGE – EDATA Page Register PAGE = 86H Reset Value = XXXX XXX0B Not Bit Addressable –––– ––– PAGE.0 Bit 7654 321 0 Symbol Function PAGE0 Selects which 256-byte page of EDATA is currently accessible by MOVX @Ri instructions. |
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