ST72F521 datasheet(213/215 Pages) STMICROELECTRONICS

213 / 215 page

ST72F521, ST72521B

213/215

KNOWN LIMITATIONS (Cont’d)

15.2 ALL FLASH DEVICES

15.2.1 Internal RC Oscillator with LVD

The internal RC can only be used if LVD is ena-

bled.

15.2.2 I/O behaviour during ICC mode entry

sequence

Symptom

In 80-pin devices (Flash), both Port G and H are

forced to output push-pull during ICC mode entry

sequence. 80-pin ROM devices are not impacted

by this issue.

Details

To enable programming of all flash sectors, the

device must leave USER mode and be configured

in ICC mode. Once in ICC mode, the ICC protocol

enables an ST7 microcontroller to communicate

with an external controller (such as a PC). ICC

mode is entered by applying 39 pulses on the IC-

CDATA signal during reset. To enter ICC mode,

the device goes through other modes, some

modes are critical because the I/Os PG[7:0] and

PH[7:0] are forced to output push-pull.

Impact on the Application

The PG and PH I/O ports are forced to output

push-pull during three pulses on ICCDATA. In cer-

tain circumstances, this behaviour can lead to a

short-circuit between the I/O signals and VDD, VSS

or an output signal of another application compo-

nent.

In addition, switching these I/Os to output mode

can cause the application to leave reset state, dis-

turbing the ICC communication and preventing the

user from programming the flash.

15.2.3 Read-out protection with LVD

The LVD is not supported if Readout protection is

enabled.

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