AN2014 datasheet(52/65 Pages) STMICROELECTRONICS

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Power supply loss and application reset

AN2014

52/65

DocID10701 Rev 10

6.1.3

MICROWIRE family

Main recommendation for MICROWIRE products is to deselect the device in a safe way.

The chip must be deselected taking care of the timings of Chip Select respect to the Clock

rising edge.

•

Smart connections of EEPROM pins help to avoid deselect critical configurations when

Master releases MICROWIRE bus. Refer to Section 4: Hardware considerations

section for safe connections. At deselect, EEPROM will go into the standby state (see

Figure 42: MICROWIRE bus enters the high impedance state (Master reset)).

•

However when deselecting the EEPROM, a write cycle may be triggered if the

EEPROM is deselected between two data bytes of a write instruction.

•

When Master restarts, it must run a data polling sequence to check that EEPROM is

ready (no write cycle in progress).

•

As soon as device is ready, an Erase/Write Disable (EWDS) instruction must be issued

to disable any WRITE instruction. In this way, the device is protected against any

parasitic WRITE instruction.

These recommendations will maximize the control on the EEPROM in case of inadvertent

Master reset. Recommendations for Master restart can also be the default sequence each

time Master comes out of the reset state like after Power up.

Figure 42. MICROWIRE bus enters the high impedance state (Master reset)

1. A pull-down resistor on C prevents any tSLCH timing violation (as a pull-up resistor on C causes C to rise at

the same time as S goes low, inducing tSLCH = 0).

Ai11092c

Safe

MICROWIRE bus connections

MICROWIRE bus waveforms when the bus enters

the high-impedance state

Safe

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