stled325 STMicroelectronics, stled325 Datasheet - Page 12

• Manufacturer Part Number: stled325
• Description: I?c Interfaced, Advanced Led Controller/driver With Keyscan, Standby Power Management And Real Time Clock Rtc
• Manufacturer: STMicroelectronics

Functional description
3.4
3.5
3.6
3.6.1
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Display types
Figure 4.
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.
Timers
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.
Display types
Seven segment display with dot point and common-anode LED panel
Doc ID 17576 Rev 1
STLED325