C511 datasheet(55/128 Pages) SIEMENS

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Semiconductor Group

6-22

On-Chip Peripheral Units

6.2.2 Timer/Counter 2 (SAB-C513/C513A/C513A-H only)

Timer 2 is a 16-bit timer / counter which can operate as timer or counter. It has 3 operating modes :

– 16-bit auto-reload mode (up or down counting)

– 16-bit capture mode

– Baudrate generator (see chapter 6.3.3.2)

The modes are selected by bits in the SFR T2CON (C8H) as shown in table 6-5.

Table 6-5

Timer/Counter 2 - Operating Modes

Timer 2 consists of two 8-bit registers, TH2 and TL2. In the timer function, the TL2 register is

incremented every machine cycle. Since a machine cycle consists of 12 oscillator periods, the count

rate is 1/12 of the oscillator frequency.

In the counter function, the register is incremented in response to a 1-to-0 transition at its

corresponding external input pin T2 (P1.0). In this function, the external input is sampled during

S5P2 of every machine cycle. When the samples show a high in one cycle and a low in the next

cycle, the count is incremented. The new value appears in the register during S3P1 of the cycle

following the one in which the transition was detected. Since it takes two machine cycles to

recognize a 1-to-0 transition, the maximum count rate is 1/24 of the oscilllator frequency. To ensure

that a given level is sampled at least once before it changes, it should be held for at least one full

machine cycle.

RCLK + TCLK

CP/RL2

TR2

Mode

16-bit auto-reload

16-bit capture

Baud rate generator

(OFF)

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