ST90R158 datasheet(101/190 Pages) STMICROELECTRONICS

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ST90158 - TIMER/WATCHDOG (WDT)

TIMER/WATCHDOG (Cont’d)

9.1.5 Register Description

The Timer/Watchdog is associated with 4 registers

mapped into Group F, Page 0 of the Register File.

WDTHR: Timer/Watchdog High Register

WDTLR: Timer/Watchdog Low Register

WDTPR: Timer/Watchdog Prescaler Register

WDTCR: Timer/Watchdog Control Register

Three additional control bits are mapped in the fol-

lowing registers on Page 0:

Watchdog Mode Enable, (WCR.6)

Top Level Interrupt Selection, (EIVR.2)

Interrupt A0 Channel Selection, (EIVR.1)

Note: The registers containing these bits also con-

tain other functions. Only the bits relevant to the

operation of the Timer/Watchdog are shown here.

Counter Register

This 16 bit register (WDTLR, WDTHR) is used to

load the 16 bit counter value. The registers can be

read or written “on the fly”.

TIMER/WATCHDOG HIGH REGISTER (WDTHR)

R248 - Read/Write

Reset value: 1111 1111 (FFh)

Bit 7:0 = R[15:8]

Counter Most Significant Bits.

TIMER/WATCHDOG LOW REGISTER (WDTLR)

R249 - Read/Write

Reset value: 1111 1111b (FFh)

Bit 7:0 = R[7:0]

Counter Least Significant Bits.

TIMER/WATCHDOG PRESCALER REGISTER

(WDTPR)

R250 - Read/Write

Reset value: 1111 1111 (FFh)

Bit 7:0 = PR[7:0]

Prescaler value.

A programmable value from 1 (00h) to 256 (FFh).

Warning: In order to prevent incorrect operation of

the Timer/Watchdog, the prescaler (WDTPR) and

counter (WDTRL, WDTRH) registers must be ini-

tialised before starting the Timer/Watchdog. If this

is not done, counting will start with the reset (un-in-

itialised) values.

WATCHDOG

TIMER

CONTROL REGISTER

(WDTCR)

R251- Read/Write

Reset value: 0001 0010 (12h)

Bit 7 = ST_SP:

Start/Stop Bit.

This bit is set and cleared by software.

0: Stop counting

1: Start counting (see Warning above)

Bit 6 = S_C:

Single/Continuous.

This bit is set and cleared by software.

0: Continuous Mode

1: Single Mode

Bit 5:4 = INMD[1:2]:

Input mode selection bits.

These bits select the input mode:

R15

R14

R13

R12

R11

R10

PR7

PR6

PR5

PR4

PR3

PR2

PR1

PR0

ST_SP

S_C

INMD1

INMD2

INEN

OUTMD

WROUT

OUTEN

INMD1

INMD2

INPUT MODE

Event Counter

Gated Input (Reset value)

Triggerable Input

Retriggerable Input

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