AT89LP428 Datasheet, PDF (11/149 Pages) ATMEL Corporation – 8-bit Microcontroller with 4K/8K Bytes In-System Programmable Flash

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
05FF
AT89LP828
3.3.1 EDATA
03FF
0200
01FF
0000
AT89LP428
Flash Data
(FDATA)
Extra RAM
(EDATA)
0200
01FF
0000
Flash Data
(FDATA)
Extra RAM
(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.
Table 3-3. PAGE – EDATA Page Register
PAGE = 86H
Reset Value = XXXX XXX0B
Not Bit Addressable
–
–
–
–
–
–
–
PAGE.0
Bit
7
6
5
4
3
2
1
0
Symbol
PAGE0
Function
Selects which 256-byte page of EDATA is currently accessible by MOVX @Ri instructions.
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