UPSD3313D-40U6 datasheet(69/231 Pages) STMICROELECTRONICS

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uPSD33xx

STANDARD 8032 TIMER/COUNTERS

There are three 8032-style 16-bit Timer/Counter

registers (Timer 0, Timer 1, Timer 2) that can be

configured to operate as timers or event counters.

There are two additional 16-bit Timer/Counters in

the Programmable Counter Array (PCA), seePCA

Block, page 123 for details.

Standard Timer SFRs

Timer 0 and Timer 1 have very similar functions,

and they share two SFRs for control:

■

TCON (Table 39., page 70)

■

TMOD (Table 40., page 72).

Timer 0 has two SFRs that form the 16-bit counter,

or that can hold reload values, or that can scale

the clock depending on the timer/counter mode:

■

TH0 is the high byte, address 8Ch

■

TL0 is the low byte, address 8Ah

Timer 1 has two similar SFRs:

■

TH1 is the high byte, address 8Dh

■

TL1 is the low byte, address 8Bh

Timer 2 has one control SFR:

■

T2CON (Table 41., page 75)

Timer 2 has two SFRs that form the 16-bit counter,

and perform other functions:

■

TH2 is the high byte, address CDh

■

TL2 is the low byte, address CCh

Timer 2 has two SFRs for capture and reload:

■

RCAP2H is the high byte, address CBh

■

RCAP2L is the low byte, address CAh

Clock Sources

When enabled in the “Timer” function, the Regis-

ters THx and TLx are incremented every 1/12 of

the oscillator frequency (fOSC). This timer clock

source is not effected by MCU clock dividers in the

CCON0, stalls from PFQ/BC, or bus transfer cy-

cles. Timers are always clocked at 1/12 of fOSC.

When enabled in the “Counter” function, the Reg-

isters THx and TLx are incremented in response to

a 1-to-0 transition sampled at their corresponding

external input pin: pin C0 for Timer 0; pin C1 for

Timer 1; or pin T2 for Timer 2. In this function, the

external clock input pin is sampled by the counter

at a rate of 1/12 of fOSC. When a logic '1' is deter-

mined in one sample, and a logic '0' in the next

sample period, the count is incremented at the

very next sample period (period1: sample=1,

period2: sample=0, period3: increment count

while continuing to sample). This means the max-

imum count rate is 1/24 of the fOSC. There are no

restrictions on the duty cycle of the external input

signal, but to ensure that a given level is sampled

at least once before it changes, it should be active

for at least one full sample period (12 / fOSC, sec-

onds). However, if MCU_CLK is divided by the

SFR CCON0, then the sample period must be cal-

culated based on the resultant, longer, MCU_CLK

frequency. In this case, an external clock signal on

pins C0, C1, or T2 should have a duration longer

than one MCU machine cycle, tMACH_CYC. The

section, Watchdog Timer, WDT, page 66 explains

how to estimate tMACH_CYC.

UPSD3313D-40U6 Datasheet(PDF) 69 Page - STMicroelectronics

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