AT89LP428 datasheet(122/149 Pages) ATMEL

122 / 149 page

122

3654A–MICRO–8/09

AT89LP428/828

23.8

User Signature and Analog Configuration

The User Signature Array contains 128 bytes of nonvolatile memory in two 64-byte pages. The

first page of the User Signature Array (0000H - 003FH) is available for serial numbers, firmware

revision information, date codes or other user parameters. The User Signature Array may only

be written by an external device when the User Signature Programming Fuse is enabled. When

the fuse is enabled, Chip Erase will also erase the first page of the array. When the fuse is dis-

abled, the array is not affected by write or erase commands. Programming of the Signature

Array can also be disabled by the Lock Bits. However, reading the signature is always allowed

and the array should not be used to store security sensitive information. The User Signature

Array may be modified during execution through the In-Application Programming interface,

regardless of the state of the User Signature Programming fuse or Lock Bits, provided that the

IAP Fuse is enabled. Note that the address of the User Signature Array, as seen by

the IAP interface, equals the User Signature address plus 128 (0080H - 00FFH instead of

0000H - 007FH).

The second page of the User Signature Array (0040H - 007FH) contains analog configuration

parameters for the AT89LP428/828. Each byte represents a parameter as listed in Table 23-

7 and is preset in the factory. The parameters are read at POR and the device is configured

accordingly. The second page of the array is not affected by Chip Erase. Other bytes in this

page may be used as additional signature space; however, care should be taken to preserve the

parameter values when modifying other bytes.

23.9

Programming Interface Timing

This section details general system timing sequences and constraints for entering or exiting In-

System Programming as well as parameters related to the Serial Peripheral Interface during

ISP. The general timing parameters for the following waveform figures are listed in section “Tim-

ing Parameters” on page 126.

23.9.1

Power-up Sequence

Execute this sequence to enter programming mode immediately after power-up. In the RST pin

is disabled or if the ISP Fuse is disabled, this is the only method to enter programming (see

“External Reset” on page 26).

Apply power between VCC and GND pins. RST should remain low.

Wait at least t

PWRUP. and drive SS high.

Wait at least t

SUT for the internal Power-on Reset to complete. The value of tSUT will

depend on the current settings of the device.

Start programming session.

Table 23-7.

Analog Configuration Definitions

Address

Parameter Name

Description

0040H

RC Oscillator Calibration Byte

The RC Calibration Byte controls the frequency of

the internal RC oscillator. The frequency is inversely

proportional to the calibration value such that higher

values result in lower frequencies. A copy of the

factory-set calibration value is stored at location

0008H of the Atmel Signature.

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