C511 datasheet(48/128 Pages) SIEMENS

48 / 128 page

On-Chip Peripheral Units

Semiconductor Group

6-15

6.2

Timers/Counters

The SAB-C511/513 microcontrollers contains two (SAB-C511/C511A) or three (SAB-C513/C513A/

C513A-H) 16-bit timers/counters which are useful in many applications for timing and counting

functions.

In timer function, the register is incremented every machine cycle. Thus one can think of it as

counting machine cycles. Since a machine cycle consists of 12 oscillator periods, the counter rate

is 1/12 of the oscillator frequency.

In counter function, the register is incremented in response to a 1-to-0 transition (falling edge) at

its corresponding external input pin, T0 or T1 (alternate functions of P3.4 and P3.5, resp.). 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 counter is incremented. The new count 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 (24 oscillator periods) to recognize a 1-to-0 transition,

the maximum count rate is 1/24 of the oscillator frequency. 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 must be held for at least one full machine cycle.

C511 Datasheet(PDF) 48 Page - Siemens Semiconductor Group