AT89LP428 datasheet(14/149 Pages) ATMEL

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3654A–MICRO–8/09

AT89LP428/828

3.4

In-Application Programming (IAP)

The AT89LP428/828 supports In-Application Programming (IAP), allowing the program memory

to be modified during execution. The IAP can be used to modify the user application on-the-fly or

to use program memory for nonvolatile data storage. The same write protocol for FDATA also

applies to IAP (see “Write Protocol” on page 12). The CPU is always placed in idle while modify-

ing the program memory. When the write completes, the CPU will continue executing with the

instruction after the MOVX @DPTR,A instruction that started the write.

To enable access to the program memory, the IAP bit (MEMCON.7) must be set to one and the

IAP User Fuse must be enabled. The IAP User Fuse can disable all IAP operations. When this

fuse is disabled, the IAP bit will be forced to 0. While IAP is enabled, all MOVX @DPTR instruc-

tions will access the CODE space instead of EDATA or FDATA. The IAP also allows

reprogramming of the User Signature Array when SIGEN = 1. The IAP access settings are sum-

marized in Table 3-5.

Table 3-4.

MEMCON

– Memory Control Register

MEMCON = 96H

Reset Value = 0000 00XXB

Not Bit Addressable

IAP

AERS

LDPG

MWEN

DMEN

ABORT

–

WRTINH

Bit

7654

3210

Symbol

Function

IAP

In-Application Programming Enable. When IAP = 1 and the IAP Fuse is enabled, programming of the CODE/SIG space

is enabled and MOVX @DPTR instructions will access CODE/SIG instead of EDATA or FDATA. Clear IAP to disable

programming of CODE/SIG and allow access to EDATA and FDATA.

AERS

Auto-Erase Enable. Set to perform an auto-erase of a Flash memory page (CODE, SIG or FDATA) during the next write

sequence. Clear to perform write without erase.

LDPG

Load Page Enable. Set to this bit to load multiple bytes to the temporary page buffer. Byte locations may not be loaded

more than once before a write. LDPG must be cleared before writing.

MWEN

Memory Write Enable. Set to enable programming of a nonvolatile memory location (CODE, SIG or FDATA). Clear to

disable programming of all nonvolatile memories.

DMEN

Data Memory Enable. Set to enable nonvolatile data memory and map it into the FDATA space. Clear to disable

nonvolatile data memory.

ABORT

Abort Flag. Set by hardware if an error occurred during the last programming sequence due to a brownout condition

(low voltage on VCC). Must be cleared by software.

WRTINH

Write Inhibit Flag.

Cleared by hardware when the voltage on V

CC has fallen below the minimum programming

voltage. Set by hardware when the voltage on V

CC is above the minimum programming voltage.

Table 3-5.

IAP Access Settings

IAP

SIGEN

DMEN

MOVX @DPTR

MOVC @DPTR

EDATA

CODE

FDATA

CODE

EDATA

SIG

FDATA

SIG

CODE

SIG

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