HPC-DEV-IBMC datasheet(15/30 Pages) NSC

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Timer Overview (Continued)

The timers T1 through T3 in conjunction with their registers

form Timer-Register pairs The registers hold the pulse du-

ration values All the Timer-Register pairs can be read from

or written to Each timer can be started or stopped under

software control Once enabled the timers count down and

upon underflow the contents of its associated register are

automatically loaded into the timer

SYNCHRONOUS OUTPUTS

The flexible timer structure of the HPC46400E simplifies

pulse generation and measurement There are four syn-

chronous timer outputs (TS0 through TS3) that work in con-

junction with the timer T2 The synchronous timer outputs

can be used either as regular outputs or individually pro-

grammed to toggle on timer T2 underflows (see

Figure 12 )

Maximum output frequency for any timer output can be ob-

tained by setting timerregister pair to zero This then will

produce an output frequency equal to

the frequency of

the source used for clocking the timer

Timer Registers

There are four control registers that program the timers The

divide by (DIVBY) register programs the clock input to tim-

ers T2 and T3 The timer mode register (TMMODE) contains

control bits to start and stop timers T1 through T3 It also

contains bits to latch acknowledge and enable interrupts

from timers T0 through T3

Timer Applications

The use of Pulse Width Timers for the generation of various

waveforms is easily accomplished by the HPC46400E

Frequencies can be generated by using the timerregister

pairs A square wave is generated when the register value is

a constant The duty cycle can be controlled simply by

changing the register value

TLDD10422 – 22

FIGURE 13 Square Wave Frequency Generation

Synchronous outputs based on Timer T2 can be generated

on the 4 outputs TS0 – TS3 Each output can be individually

programmed to toggle on T2 underflow Register R2 con-

tains the time delay between events

Figure 14 is an exam-

ple of synchronous pulse train generation

TLDD10422 – 23

FIGURE 14 Synchronous Pulse Generation

WATCHDOG Logic

The WATCHDOG Logic monitors the operations taking

place and signals upon the occurrence of any illegal activity

The illegal conditions that trigger the WATCHDOG logic are

potentially infinite loops Should the WATCHDOG register

not be written to before Timer T0 overflows twice or more

often than once every 4096 counts an infinite loop condi-

tion is assumed to have occurred The illegal condition

forces the Watch Out (WO) pin low The WO pin is an open

drain output and can be connected to the RESET or NMI

inputs or to the users external logic

MICROWIREPLUS

MICROWIREPLUS is used for synchronous serial data

communications (see

Figure 15 ) MICROWIREPLUS has

an 8-bit parallel-loaded serial shift register using SI as the

input and SO as the output SK is the clock for the serial

shift register (SIO) The SK clock signal can be provided by

an internal or external source The internal clock rate is pro-

grammable by the DIVBY register A DONE flag indicates

when the data shift is completed

The MICROWIREPLUS capability enables it to interface

with any of National Semiconductor’s MICROWIRE periph-

erals (ie ISDN Transceivers AD converters display driv-

ers EEPROMs)

TLDD10422 – 24

FIGURE 15 MICROWIREPLUS

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