AT89LP428-20MU ATMEL [ATMEL Corporation], AT89LP428-20MU Datasheet - Page 11

• Manufacturer Part Number: AT89LP428-20MU
• Description: 8-bit Microcontroller with 4K/8K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

3.3
3.3.1
3654A–MICRO–8/09
External Data Memory
EDATA
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
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.
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.
Symbol
PAGE0
PAGE = 86H
Not Bit Addressable
Bit
03FF
01FF
0200
0000
Function
Selects which 256-byte page of EDATA is currently accessible by MOVX @Ri instructions.
External Data Memory Map
PAGE
–
7
– EDATA Page Register
AT89LP428
Flash Data
Extra RAM
(EDATA)
(FDATA)
–
6
–
5
–
4
–
3
Figure
05FF
01FF
0200
0000
3-3. These memory spaces may
Reset Value = XXXX XXX0B
–
2
AT89LP428/828
AT89LP828
Flash Data
Extra RAM
(FDATA)
(EDATA)
–
1
PAGE.0
0
11