STFPC320 datasheet(18/78 Pages) STMICROELECTRONICS

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Functional description

STFPC320

18/78

4.7

Mute pin

The MUTE pin is set to logic high to mute the audio output before power is cut to the host

processor. In wakeup mode, the MUTE pin is set to logic low to enable the audio output

immediately after the high assertion of the READY pin. In general, MUTE follows READY pin

with an inverted polarity. This pin is used to prevent pop-up sound during power-up and

power-down states.

4.8

Keyscan matrix/front panel keys

The key scan matrix on the STFPC320 helps to pass command from the front panel to the

host processor through the SDA pin on STFPC320. The STFPC320 can be programmed to

wake-up the system from standby using any of the 24 keys pressed on the front panel.

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

4.9

LED ports

4 LED displays are supported by the STFPC320. Turning on or off of the LED is done by

issuing write command to the LED port. After reset, the LEDs are off. Note that the LED

outputs sink the current, so the cathode of the diode must be connected to the LED pins of

STFPC320.

4.10

Display

The display is divided into two sections, Normal and real-time clock (RTC).

4.10.1

Normal display

The VFD display is configurable for displays from 8 digits/20 segments to 16 digits/12

segments. The VFD display can be configured to be either in the normal VFD mode or in the

RTC mode. In the normal VFD mode, the display shows whatever is written in the VFD

display memory.

If the user desires to show normal display simultaneously with the RTC, then CPU must

read the time of RTC display memory and then write all the data to be displayed to the

normal display memory. After writing the values to the display memory, a display-on

command will show both the normal and RTC display on the front panel.

On first power on, the default configuration is 16-digit, 12-segment mode (with display

turned OFF).

4.10.2

RTC display

In RTC mode, the display can be configured to show the time in two modes, either by direct

mapping of RTC to the display or by using the CPU. If CPU is used, the CPU reads the RTC

value from RTC registers and then writes the time to be displayed in the RTC display

memory.

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