MCS51 - lecture 3. Lecture 3 2/30 Timers/counters MCS51.

MCS51 - lecture 3

Lecture 3 2/30

Timers/counters MCS51

MCS51 - timer/counter #0 i #1 3/30

Common features:

• 16-bit;

• accessible in SFR as register pairs THx-TLx;

• counting up;

• count machine cycles (timer mode) or external pulses (counter mode);

• external pulses can be gated;

• controlled by special registers in SFR;

• overflow (from 0FFFF to 0) sets TFx flag, which can cause interrupt;

• 3 the same working mode: 0, 1 i 2.

Timer/counter #0 can also work in mode 3, then timer/counter #1 is stopped.


GATE C/T M1 M0 GATE C/T M1 M0TMOD 89h

Control registers:

timer/counter #1 timer/counter #0

GATE - set - enables gating of external pulses;

C/T - set - counter mode, cleared - timer mode;

M1,M0 - select one of working mode:

timer/counter #1 timer/counter #0

0 0 - mode 0 0 0 - mode 0 (13-bit)

0 1 - mode 1 0 1 - mode 1 (16-bit)

1 0 - mode 2 1 0 - mode 2 (8-bit with reload)

1 1 - disabled 1 1 - mode 3 (double 8-bit)


TF1 8F TR1 8E TF0 8D TR0 8C IE1 8B IT1 8A IE0 89 IT0 88TCON 88h

TF1 - timer/counter #1 overflow flag

TR1 - set - starts timer/counter 1

TF0 - timer/counter #0 overflow flag

TR0 - set - starts timer/counter 0

8AhTL08BhTL18ChTH08DhTH1

Value registers:


Mode 0 - 13-bit

OSC

TLx 5b THx 8b

:12

TRx

C/T

GATE

TFx

Tx

INTx

0

1

0

1


Mode 1 - 16-bit

OSC

TLx 8b THx 8b

:12

TRx

C/T

GATE

TFx

Tx

INTx

0

1

0

1


Mode 2 - 8-bit with automatic reload

OSC

TLx 8b

THx 8b

:12

TRx

C/T

GATE

TFx

Tx

INTx

0

1

0

1


Timer/counter #0 mode 3 - double 8-bit

OSC

TL0 8b

TH0 8b:12

TR0

C/T

GATE

TF0

Tx

INT0

0

1

0

1

TF10

1

TR1


Counting external pulses (C/T=1):

• counted falling edges;

• falling edge on input Tx is detected, if during one machine cycle there is a high level and in the next - low;

• increment of counter content is done in machine cycle following detected edge;

• maximal frequency of counted pulses = fCLK:24.

machine cycle N-1 machine cycle N machine cycle N+1

detection of falling edge

counterincrement

3/4m.c. 3/4m.c. 1/3m.c.


Possible applications of timer/counter #0 & #1:

• time interval measure with time-end signalled by interrupt or only TFx flag;

• clock interrupt;

• in 8-bit mode with automatic reload on fCLK=12MHz clock interrupt period up to 256s (3,9kHz);

• in 16-bit mode with program reload on fCLK=12MHz clock interrupt period up to 65,5ms (15,25Hz);

• counting external pulses/events.;

• counting programmed number of pulses and interrupt request;

• clocking of SIO - only timer #1 !.

MCS51 - timer/counter #2 12/30

Features:

• 16-bit;

• accessible in SFR as register pair TH2-TL2;

• counting up;

• count machine cycles (timer mode) or external pulses (counter mode);

• 16-bit compare-capture register RCAP2H-RCAP2L;

• controlled by special registers in SFR;

• overflow (from 0FFFF to 0) sets TF2 flag, which can cause interrupt;

• can clock SIO;


Control register:

TF2 CF EXF2CE RCLKCD TCLKCC EXEN2CB TR2 CA C/T2 C9 CP/RL2C8T2CON C8h

TF2 - timer/counter #2 overflow flag, set by hardware after counter overflow only if bits RCLK i TCLK are cleared

EXF2 - falling edge on input T2EX (P1.1) flag, acting only if bit EXEN2=1

EXEN2 - if set enables detecting of falling edge on T2EX input for example to capture/reload counter

TR2 - if set starts timer/counter #2

C/T2 - set - counter mode, cleared - timer mode

CP/RL2 - set - capture mode, cleared - reload mode

RCLK, TCLK - if set, TF2 flag clocks SIO receiver & transmitter if cleared, timer/counter 1 clocks SIO


Work with automatic capture on CP/RL2=1 TCLK=RCLK=0

OSC

TL2 TH2

:12

TR2

C/T2

EXEN2

TF2

T2

T2EX

0

1

0

1

RCAP2L RCAP2H

EXF20

1


Work with automatic reload on CP/RL2=0 TCLK=RCLK=0

OSC

TL2 TH2

:12

TR2

C/T2

EXEN2

TF2

T2

T2EX

0

1

0

1

RCAP2L RCAP2H

EXF20

1


Work as SIO clock on RCLK=1 or TCLK=1

OSC

TL2 TH2

:2

TR2

C/T2

EXEN2

TF1

T2

T2EX

0

1

0

1

RCAP2L RCAP2H

EXF20

1

:2

:16

:16

RxC

TxC

SMOD

RCLK

TCLK

0 1

1 0

1 0


Possible applications of timer/counter #2:

• time interval measure with time-end signalled by interrupt or only TF2 flag;

• clock interrupt;

• 16-bit reload constant allows to achieve long period of clock interrupt;

• counting external pulses/events;

• counting programmed number of external pulses and interrupt request;

• independent SIO receiver & transmitter clocking;

• SIO clocking in wide range of frequency;

• measure of phenomenon duration, which begin and end are signalled by falling edge on T2EX.

MCS51 - timer/counter #2 - other modifications 18/30

Work with automatic reload & rectangular waveform output on T2

0

1

OSCTL2 TH2

:2

TR2

C/T2

EXEN2

optionaldo SIO

T2

T2EX

0

1

RCAP2L RCAP2H

EXF20

1

:2

T2OE

0

1

fOUT=fOSC/4/(65536-RCAP2)

MCS51 - timer/counter #2 - other modifications 19/30

0FFh 0FFh

OSC

TL2 TH2

:12

TR2

C/T2

TF2

T2

T2EX

0

1

0

1

RCAP2L RCAP2H

EXF2

0

1

counting direction: 0 - down; 1 - up

counting up: from RCAP2 value up to 0FFFFhcounting down: from 0FFFFh down to RCAP2 value

Work with automatic reload & switched counting direction (up/down)

MCS51 - PCA 20/30

PCA - Programmable Counter Array

Features:

• 16-bit counter accessible in SFR as register pair CH-CL, working as common time base for 5 units;

• counting up;

• can counts: divided internal clock pulses or external pulses or timer/counter 0 output pulses;

• 5 16-bit compare-capture units CCAPxH-CCAPxL;

• each unit can work in mode: capture, timing, PWM, pulse generation;

• one unit can work as watch-dog;

• interrupt request possible;

MCS51 - PCA 21/30

Main counter structure - time base

IDLCIDL

ECF

CR

CPS0CPS1

OSC :4

:3

ECI

T0OVCL CH CF

CCU#0..#4

interruptsystem

0

1

MCS51 - PCA 22/30

Unit in capture mode

CCAPnL CCAPnH

CCFn interrupt systemECCFn

CEXn

0

1

0

1

CAPPnCAPNn

CL CH

MCS51 - PCA 23/30

Unit in timing mode

CCAPnL CCAPnH

CL CH

0

1

MATn

CCFn interruptsystem

ECCFn

E =? EQECOMn

write toCCAPnL

write toCCAPnH RESET

0 1

MCS51 - PCA 24/30

Unit in pulse generation mode

CCAPnL CCAPnH

CL CH

0

1

MATn

CCFn interruptsystem

ECCFn

E =? EQECOMn

write toCCAPnL

write toCCAPnH RESET

0 1

0

1

TOGn

CEXn

MCS51 - PCA 25/30

Unit in PWM mode

CCAPnL

CCAPnH

CL OV

PWMn CL<CCAPnLE =?

CL>CCAPnLECOMn

0

1

CEXn

MCS51 - PCA 26/30

Unit #4 as watch-dog

CCAP4L CCAP4H

CL CH

0

1

WDTE

RESETE =? EQECOM4

write toCCAP4L

write toCCAP4H RESET

0 1

MCS51 - PCA 27/30

Possible applications of PCA:

• parallel execution up to 5 task synchronized by common time-base counter;

• simultaneous, 5-channel measure of phenomenon duration.

MCS51 - CCU Philips 28/30

OSCTL2 TH2

:12

T2ER

T2MS1,T2MS0

T2OV

T2

RT2

0001

11

0 1CM0

external counter clear

T2P1,T2P0

:1/:2:4/:8

T2BO

CML0

CMH0=?

CML1

CMH1

CML2

CMH2

=?

=?

CM1

CM2

CTL0 CTH0

CT0ICTI0

CTL1 CTH1

CT1ICTI1

CTL2 CTH2

CT2ICTI2

CTL3 CTH3

CT3ICTI3

MCS51 - CCU Siemens 29/30

Structure of CCU in 515, 515A of Siemens

CCL1+CCH1

CCL2+CCH2

CCL3+CCH3

P1

CRCL+CRCH

counter T2

prescaler OSC

MCS51 - CCU Siemens 30/30

Timer #2 structure in Siemens MCU with CCU

CRCL CRCH

TL2 TH2

EXF2

TF2

EXEN2

T2R0

T2R1

T2I0T2PS1T2PS0

OSC :12 PRESKALER:1 :2 :4 :8

T2I1

T2EX

T2

to interrupt

system

MCS51 - lecture 3. Lecture 3 2/30 Timers/counters MCS51.

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