ST72E121 datasheet(23/92 Pages) STMICROELECTRONICS

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ST72E121 ST72T121

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 6.

Table 6. EI2 and EI3 External Interrupt Polarity

Options

Note: Any modification of one of these two bits re-

sets the interrupt request related to this interrupt

vector.

Bit 5 = MCO

Main Clock Out

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

enables the output of the Internal Clock on the

PPF0 I/O port.

0 - PF0 is a general purpose I/O port.

1 - MCO alternate function (fCPU is output on PF0

pin).

Bit 4:3 = PEI[1:0]

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 7.

Table 7. EI0 and EI1 External Interrupt Polarity

Options

Note: Any modification of one of these two bits re-

sets the interrupt request related to this interrupt

vector.l

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 8. 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

PSM[1:0] 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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