MC908AZ32ACFUE Datasheet, PDF (223/324 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 20
Programmable Interrupt Timer (PIT)
20.1 Introduction
This section describes the Programmable Interrupt Timer (PIT) which is a periodic interrupt timer whose
counter is clocked internally via software programmable options. Figure 20-1 is a block diagram of the
PIT.
20.2 Features
Features of the PIT include:
• Programmable PIT Clock Input
• Free-Running or Modulo Up-Count Operation
• PIT Counter Stop and Reset Bits
20.3 Functional Description
Figure 20-1 shows the structure of the PIT. The central component of the PIT is the 16-bit PIT counter
that can operate as a free-running counter or a modulo up-counter. The counter provides the timing
reference for the interrupt. The PIT counter modulo registers, PMODH–PMODL, control the modulo value
of the counter. Software can read the counter value at any time without affecting the counting sequence.
INTERNAL
BUS CLOCK
PRESCALER
CSTOP
CRST
16-BIT COUNTER
PRESCALER SELECT
PPS2 PPS1 PPS0
16-BIT COMPARATOR
TIMPMODH:TIMPMODL
Figure 20-1. PIT Block Diagram
POF
INTER-
RUPT
POIE
LOGIC
MC68HC908AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
223