ST92195C4 datasheet(80/249 Pages) STMICROELECTRONICS

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ST92195C/D - TIMER/WATCHDOG (WDT)

TIMER/WATCHDOG (Cont’d)

7.1.5 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)

Bits 7:0 = R[15:8]

Counter Most Significant Bits.

TIMER/WATCHDOG LOW REGISTER (WDTLR)

R249 - Read/Write

Reset value: 1111 1111b (FFh)

Bits 7:0 = R[7:0]

Counter Least Significant Bits.

TIMER/WATCHDOG PRESCALER REGISTER

(WDTPR)

R250 - Read/Write

Reset value: 1111 1111 (FFh)

Bits 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

(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

Bits 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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