STLED325 datasheet(12/62 Pages) STMICROELECTRONICS

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Functional description

STLED325

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Doc ID 17576 Rev 1

3.4

Display types

Figure 4.

Display types

3.5

Keyscan

The full keyscan is illustrated in the later section of the datasheet. One diode is required per

key switch. The keyscan circuit detects any combination of keys being pressed during each

de-bounce cycle.

The keyscan matrix on the STLED325 passes command from the front panel to the host

processor through the SDA pin on STLED325. The STLED325 can be programmed to

wake-up the system from standby using any of the 16 keys pressed on the front panel.

These wake-up keys are also referred to as hot-keys.

3.6

Timers

3.6.1

Guard timer

For safety related applications, a guard timer is integrated in the STLED325. The guard

timer gives enhanced reliability to the device.

The guard timer can be used to detect an out of-control microprocessor. The user programs

the guard timer by setting the desired amount of time-out into the Guard timer. This guard

time has an initial de-fault value of 10s upon first power-up and subsequently can be

configured from 1s to 15s during normal operation. If a time period of longer than 15s is

desired, then the watchdog timer from RTC can be used. It can also be disabled after first

power-up. If the processor does not clear the timer within the specified period, the

STLED325 puts the system in the standby mode.

This is only active from L to H transition on READY or WAKE_UP pin but it is not level-

based. The guard timer count is cleared by the guard timer clear/reset bit. While in normal

mode, the count starts from the previously count value that was in the register. During the

cold boot up or warm boot up, the count starts from the configured value.

Seven segment display with dot point and common-anode LED panel

STLED325 Datasheet(PDF) 12 Page - STMicroelectronics