PSD211R datasheet(21/51 Pages) STMICROELECTRONICS

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PSD211R Family

12.0

Control Signals

(Cont.)

Internal Signal State

Component

Internal Signal

During Power-Down

PAD A and PAD B

CS0–CS10

Logic 1 (inactive)

CSIOPORT, ES0–ES7

Logic 0 (inactive)

All registers in CSIOPORT address

N/A

space, including:

Direction

Data

All unchanged

PMR (turbo bit, ZPSD only)

Table 7B. Internal States During Power-down

NOTE: N/A = Not Applicable

12.6 Reset Input

This is an asynchronous input to initialize the PSD device.

Refer to tables 8A and 8B for information on device status during and after reset.

The standard-voltage PSD211R and ZPSD211R (non-V) devices require a reset input. In

this case, the reset input must be asserted for at least 100 nsec. The PSD will be functional

immediately after reset is de-asserted. For these standard-voltage devices, the polarity of

the reset input signal is programmable using PSDsoft (active-high or active-low), to match

the functionality of your MCU reset.

Note: It is not recommended to drive the reset input of the MCU and the reset input of the

PSD with a simple RC circuit between power on ground. The input threshold of the MCU

and the PSD devices may differ, causing the devices to enter and exit reset at different

times because of slow ramping of the signal. This may result in the PSD not being opera-

tional when accessed by the MCU. It is recommended to drive both devices actively. A

supervisory device or a gate with hysteresis is recommended.

For low-voltage ZPSD211RV devices only, the reset input must be asserted for at least

500 nsec. The ZPSD211RV will not be functional for an additional 500 nsec after reset is

de-asserted (see Figure 8). These low voltage ZPSD211RV devices require an active-low

polarity signal for reset. Unlike the PSD211R, the polarity of the reset input is not

programmable for the ZPSD211RV. If your MCU operates with an active high reset, you

must invert this signal before driving the ZPSD211RV reset input.

You must design your system to ensure that the PSD comes out of reset and the PSD

is active before the MCU makes its first access to PSD memory. Depending on the

characteristics and speed of your MCU, a delay between the PSD reset and the MCU reset

may be needed.

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