ST72311 datasheet(24/94 Pages) STMICROELECTRONICS

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ST72311

3.5 MISCELLANEOUS REGISTER

The Miscellaneous register allows to select the

SLOW operating mode, the polarity of external in-

terrupt requests and to output the internal clock.

—

Read /Write

Reset Value: 0000 0000 (00h)

Bit 7:6 = PEI[3:2] External Interrupt EI3 and EI2

Polarity Options.

These bits are set and cleared by software. They

determine which event on EI2 and EI3 causes the

external interrupt according to Table 7.

Table 7. EI2 and EI3 External Interrupt Polarity

Options

Bit 5 = MCO Main Clock Out

This bit is set and cleared by software. When set it

allows to output the Internal Clock on PF0 I/O.

0 - PF0 is a normal I/O port.

1 - fCPU outputs on PF0 pin.

Bit 4:3 = PEI1-PEI0 External Interrupt EI1 and EI0

Polarity Options.

These bits are set and cleared by software. They

determine which event on EI0 and EI1 causes the

external interrupt according to Table 8.

Table 8. EI0 and EI1 External Interrupt Polarity

Options

Bit 2:1 = PSM[1:0] Prescaler for Slow Mode

These bits are set and cleared by software. They

determine the CPU clock when the SMS bit is set

according to the following table.

Table 9. fCPU Value in Slow Mode

Bit 0 = SMS Slow Mode Select

This bit is set and cleared by software.

0: Normal Mode - fCPU = fOSC/ 2

(Reset state)

1: Slow Mode - the fCPU value is determined by the

PSM1 and PSM0 bits.

PEI3 PEI2 MCO PEI1 PEI0 PSM1

PSM0 SMS

MODE

PEI3

PEI2

Falling edge and low level

(Reset state)

Falling edge only

Rising edge only

Rising and falling edge

MODE

PEI1

PEI0

Falling edge and low level

(Reset state)

Falling edge only

Rising edge only

Rising and falling edge

fCPU Value

PSM1

PSM0

fOSC / 4

fOSC / 16

fOSC / 8

fOSC / 32

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