ST72321BR9-AUTO View Datasheet(PDF) - STMicroelectronics

Part Name

Description

MFG CO.

ST72321BR9-AUTO

8-bit MCU for automotive with 32 to 60 Kbyte Flash/ROM, ADC, 5 timers, SPI, SCI, I2C interface

STMicroelectronics 

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ST72321Bxxx-Auto

Supply, reset and clock management

6.3

Caution:

Phase locked loop

If the clock frequency input to the PLL is in the range 2 to 4 MHz, the PLL can be used to

multiply the frequency by two to obtain an fOSC2 of 4 to 8 MHz. The PLL is enabled by option

byte. If the PLL is disabled, then fOSC2 = fOSC/2.

The PLL is not recommended for applications where timing accuracy is required (see

Section 19.5.5: PLL characteristics on page 202).

Figure 10. PLL block diagram

fOSC

PLL x 2

/2

0

fOSC2

1

PLL OPTION BIT

6.4

Multi-oscillator (MO)

Caution:

The main clock of the ST7 can be generated by three different source types coming from the

multi-oscillator block:

● an external source

● 4 crystal or ceramic resonator oscillators

● an internal high frequency RC oscillator

Each oscillator is optimized for a given frequency range in terms of consumption and is

selectable through the option byte. The associated hardware configurations are shown in

Table 9. Refer to Chapter 19: Electrical characteristics for more details.

The OSC1 and/or OSC2 pins must not be left unconnected. For the purposes of Failure

Mode and Effect Analysis, it should be noted that if the OSC1 and/or OSC2 pins are left

unconnected, the ST7 main oscillator may start and, in this configuration, could generate an

fOSC clock frequency in excess of the allowed maximum (> 16 MHz), putting the ST7 in an

unsafe/undefined state. The product behavior must therefore be considered undefined when

the OSC pins are left unconnected.

External clock source

In this external clock mode, a clock signal (square, sinus or triangle) with ~50% duty cycle

has to drive the OSC1 pin while the OSC2 pin is tied to ground.

Crystal/ceramic oscillators

This family of oscillators has the advantage of producing a very accurate rate on the main

clock of the ST7. The selection within a list of four oscillators with different frequency ranges

has to be done by option byte in order to reduce consumption (refer to Section 21.1.1: Flash

configuration on page 228 for more details on the frequency ranges). In this mode of the

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