SZF2002 datasheet(18/76 Pages) PHILIPS

18 / 76 page

1998 Aug 26

Philips Semiconductors

Product speciﬁcation

Low voltage 8-bit microcontroller with

6-kbyte embedded RAM

SZF2002

12 TIMER/EVENT COUNTERS

The SZF2002 contains three 16-bit timer/event counter

registers; Timer 0, Timer 1 and Timer 2 which can perform

the following functions:

• Measure time intervals and pulse duration

• Count events

• Generate interrupt requests.

In the ‘Timer’ operating mode the register increments

every machine cycle. Since a machine cycle consists of

6 clock periods, the count rate is 1

⁄6fclk.

In the ‘Counter’ operating mode, the register increments in

response to a HIGH-to-LOW transition. Since it takes

2 machine cycles (12 clock periods) to recognize a

HIGH-to-LOW transition, the maximum count rate is

⁄12fclk. To ensure a given level is sampled, it should be

held for at least one complete machine cycle.

12.1

Timer 0 and Timer 1

Timer 0 and Timer 1 can be programmed independently to

operate in four modes:

Mode 0 8-bit timer or 8-bit counter each with divide-by-32

prescaler.

Mode 1 16-bit time-interval or event counter.

Mode 2 8-bit time-interval or event counter with automatic

reload upon overflow.

Mode 3 Timer 0 establishes TL0 and TH0 as two

separate counters.

12.2

Timer 2

Timer 2 is a 16-bit timer/up-down counter that can operate

(like Timer 0 and 1) either as a timer or as an event

counter. These functions are selected by the state of the

C/T2 bit in the T2CON register; see Section 12.3.

Three operating modes are available: Capture,

Auto-reload and Baud Rate Generator, which also are

selected via the T2CON register.

12.2.1

CAPTURE MODE

Figure 9 shows the Capture mode. Two options in this

mode may be selected by the EXEN2 bit in T2CON:

• If EXEN2 = 0, then Timer 2 is a 16-bit timer or counter

that sets the Timer 2 overflow bit (TF2) on overflow, this

can be used to generate an interrupt.

• If EXEN2 = 1, Timer 2 operates as already described

but with the additional feature that a HIGH-to-LOW

transition at external input T2EX causes the current

value in TL2 and TH2 to be captured into registers

RCAP2L and RCAP2H respectively. In addition, the

transition at T2EX causes the EXF2 bit in T2CON to be

set; this may also be used to generate an interrupt.

12.2.2

AUTO-RELOAD MODE

Figure 10 shows the Auto-reload mode.

• Counting up (DCEN = 0)

In the Auto-reload mode and counting up, registers

RCAP2L/RCAP2H are used to hold a reload value for

TL2 /TH2 when Timer 2 rolls over. By setting/clearing bit

EXEN2 in T2CON the external trigger input pin T2EX

can be enabled/disabled. If EXEN2 = 0, then Timer 2 is

a 16-bit timer/counter which upon overflow sets TF2,

and reloads TL2/TH2 with the reload value held in

RCAP2L/RCP2H. If EXEN2 = 1, then Timer 2 performs

as above, but with the added feature that a

HIGH-to-LOW transition at pin T2EX causes the current

Timer 2 value (TL2/TH2 data) to be reloaded with the

value held in RCAP2L/RAP2H, and bit EXF2 in T2CON

to be set.

Timer 2 interrupt will be set if EXF2 is set or TF2 is set.

• Counting up (DCEN = 1 and T2EX = 1). In this mode

Timer 2 will count up. When the timer overflows (FFFFH

state), TF2 bit will be set. This will reload TL2 and TH2

with the contents of T2CAPL and T2CAPH, respectively.

Also bit EXF2 will be toggled. Bit EXF2 can be used as

the 17th bit if desired.

Timer 2 interrupt will be set only if TF2 is set.

• Counting down (DCEN = 1 and T2EX = 0. In this mode

Timer 2 will be counting down. Underflow will occur

when the contents of TL2/TH2 matches the contents of

RCAP2L/RCAP2H. A Timer 2 roll-over from

0000H to FFFFH is not considered as an underflow.

Upon underflow, bit TF2 will be set and registers

TL2/TH2 will be loaded with FFFFH. In addition, an

underflow will cause bit EXF2 to toggle, such that it can

be used as the 17th bit if desired.

Timer 2 interrupt will be set only if TF2 is set.

12.2.3

BAUD RATE GENERATOR MODE

The Baud Rate Generator mode is selected when

RCLK0 = 1 or TCLK0 = 1 or RCLK1 = 1 or TCLK1 = 1.

It will be described in conjunction with the serial port

(UART); see Section 17.3.2.

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