Overview - Fujitsu 8FX Hardware Manual

CHAPTER 11 8/16-BIT COMPOSITE TIMER

11.1 Overview

11.1 Overview
The 8/16-bit composite timer consists of two 8-bit counters. It can be used as
two 8-bit timers, or as a 16-bit timer if the two counters are connected in
cascade.
The 8/16-bit composite timer has the following functions:
• Interval timer function
• PWM timer function
• PWC timer function (pulse width measurement)
• Input capture function
■ Interval Timer Function (One-shot Mode)
When the interval timer function (one-shot mode) is selected, the counter starts counting from
"0x00" as the timer is started. When the counter value matches the value of the 8/16-bit
composite timer data register, the timer output is inverted, an interrupt request occurs, and the
counter stops counting.
■ Interval Timer Function (Continuous Mode)
When the interval timer function (continuous mode) is selected, the counter starts counting
from "0x00" as the timer is started. When the counter value matches the value of the 8/16-bit
composite timer data register, the timer output is inverted, an interrupt request occurs, and the
counter counts from "0x00" again. The timer outputs square wave as a result of this repeated
operation.
■ Interval Timer Function (Free-run Mode)
When the interval timer function (free-run mode) is selected, the counter starts counting from
"0x00". When the counter value matches the value of the 8/16-bit composite timer data
register, the timer output is inverted and an interrupt request occurs. Under these conditions, if
the counter continues to count and reaches "0xFF", it restarts counting from "0x00". The timer
outputs square wave as a result of this repeated operation.
■ PWM Timer Function (Fixed-cycle Mode)
When the PWM timer function (fixed-cycle mode) is selected, a PWM signal with a variable
"H" pulse width is generated in fixed cycles. The cycle is fixed at "0xFF" in 8-bit operation or
at "0xFFFF" in 16-bit operation. The time is determined by the count clock selected. The "H"
pulse width is specified by setting a specific register.
■ PWM Timer Function (Variable-cycle Mode)
When the PWM timer function (variable-cycle mode) is selected, two 8-bit counters are used to
generate an 8-bit PWM signal of variable cycle and duty depending on the cycle and "L" pulse
width specified by registers.
In this operating mode, since the two 8-bit counters have to be used separately, the composite
timer cannot operate as a 16-bit counter.
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