ST72589BW datasheet(21/158 Pages) STMICROELECTRONICS

21 / 158 page

ST72589BW, ST72389BW

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MAIN CLOCK CONTROLLER (Cont’d)

MISCELLANEOUS REGISTER 2 (MISCR2)

See description in MISCELLANEOUS Register

Section.

MAIN CLOCK CONTROL/STATUS REGISTER

(MCCSR)

Read /Write

Reset Value: 0000 0000 (00h)

Bit 0 = SMS

Slow mode select

This bit is set and cleared by software.

0: Normal mode. fCPU = fOSC / 2

1: Slow mode. fCPU is given by CP1, CP0

See low power consumption mode and MCC

chapters for more details.

Bit 2:1 = CP1-CP0

CPU clock prescaler

These bits select the CPU clock prescaler which is

applied in the different slow modes. Their action is

conditioned by the setting of the SMS bit. These

two bits are set and cleared by software

Bit 4 = Reserved, always read as 0.

Bit 3:2 = TB1-TB0

Time base control

These bits select the programmable divider time

base. They are set and cleared by software.

A modification of the time base is taken into ac-

count at the end of the current period (previously

set) to avoid unwanted time shift. This allows to

use this time base as a real time clock.

Bit 1 = OIE

Oscillator interrupt enable

This bit set and cleared by software.

0: Oscillator interrupt disable

1: Oscillator interrupt enable

This interrupt allows to exit from ACTIVE-HALT

mode. When this bit is set, calling the ST7 soft-

ware HALT instruction accesses the ACTIVE-

HALT power saving mode.

Bit 0 = OIF

Oscillator interrupt flag

This bit is set by hardware and cleared by software

reading the CSR register. It indicates when set

that the main oscillator has measured the selected

elapsed time (TB1:0).

0: timeout not reached

1: timeout reached

Warning: BRES and BSET instructions must not

be used on the MCCSR register to avoid unwant-

ed clearing of OIF bit.

SMS

CP1

CP0

TB1

TB0

OIE

OIF

fCPU in SLOW mode

CP1

CP0

fOSC / 4

fOSC / 8

fOSC / 16

fOSC / 32

Counter

Prescaler

Time Base

TB1

TB0

fOSC=8MHz

fOSC=16MHz

32000

4ms

2ms

64000

8ms

4ms

160000

20ms

10ms

400000

50ms

25ms

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