80C575 Datasheet, PDF(15/40 Page) NXP Semiconductors – 80C51 8-bit microcontroller family 8K/256 OTP/ROM/ROMless, 4 comparator, failure detect circuitry, watchdog timer

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80C575 Datasheet, PDF (15/40 Pages) NXP Semiconductors – 80C51 8-bit microcontroller family 8K/256 OTP/ROM/ROMless, 4 comparator, failure detect circuitry, watchdog timer

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Philips Semiconductors

80C51 8-bit microcontroller family

8K/256 OTP/ROM/ROMless, 4 comparator, failure detect circuitry, watchdog timer

Product specification

80C575/83C575/

87C575

WRITE TO

CCAPnH RESET

WRITE TO

CCAPnL

ENABLE

ââ

CCF4

CCF3

CCF2

CCF1

CCF0

CCON

(D8H)

CCAPnH

CCAPnL

(TO CCFn)

PCA INTERRUPT

16âBIT COMPARATOR

MATCH

PCA TIMER/COUNTER

TOGGLE

CEXn

ââ

ECOMn CAPPn CAPNn MATn

TOGn

PWMn

ECCFn

CCAPMn, n: 0..4

(DAH â DEH)

Figure 11. PCA High Speed Output Mode

SU00751

Pulse Width Modulator Mode

All of the PCA modules can be used as PWM

outputs. Figure 12 shows the PWM function.

The frequency of the output depends on the

source for the PCA timer. All of the modules

will have the same frequency of output

because they all share the PCA timer. The

duty cycle of each module is independently

variable using the moduleâs capture register

CCAPLn. When the value of the PCA CL

SFR is less than the value in the moduleâs

CCAPLn SFR the output will be low, when it

is equal to or greater than the output will be

high. When CL overflows from FF to 00,

CCAPLn is reloaded with the value in

CCAPHn. the allows updating the PWM

without glitches. The PWM and ECOM bits in

the moduleâs CCAPMn register must be set

to enable the PWM mode.

WATCHDOG TIMER

The watchdog timer is not directly loadable

by the user. Instead, the value to be loaded

into the main timer is held in an autoload

programming. In order to cause the main

timer to be loaded with the appropriate value,

a special sequence of software action must

take place. This operation is referred to as

feeding the watchdog timer.

To feed the watchdog, two instructions must

be sequentially executed successfully. No

intervening instruction fetches are allowed,

so interrupts should be disabled before

feeding the watchdog. The instructions

should move A5H to the WFEED1 register

and then 5AH to the WFEED2 register. If

WFEED1 is correctly loaded and WFEED2 is

not correctly loaded, then an immediate

underflow will occur.

The watchdog timer subsystem has two

modes of operation. Its principal function is a

watchdog timer. In this mode it protects the

system from incorrect code execution by

causing a system reset when the watchdog

timer underflows as a result of a failure of

software to feed the timer prior to the timer

reaching its terminal count. If the user does

not employ the watchdog function, the

watchdog subsystem can be used as a timer.

In this mode, reaching the terminal count sets

a flag. In most other respects, the timer mode

possesses the characteristics of the

watchdog mode. This is done to protect the

integrity of the watchdog function.

The watchdog timer subsystem consists of a

prescaler and a main counter. The prescaler

has 8 selectable taps off the final stages and

the output of a selected tap provides the

clock to the main counter. The main counter

is the section that is loaded as a result of the

software feeding the watchdog and it is the

section that causes the system reset

(watchdog mode) or time-out flag to be set

(timer mode) if allowed to reach its terminal

count.

Programming the Watchdog Timer

Both the EPROM and ROM devices have a

set of SFRs for holding the watchdog

autoload values and the control bits. The

watchdog time-out flag is present in the

watchdog control register and operates the

same in all versions. In the EPROM device,

the watchdog parameters (autoload value

and control) are always taken from the SFRs.

In the ROM device, the watchdog parameters

can be mask programmed or taken from the

SFRs. The selection to take the watchdog

parameters from the SFRs or from the mask

programmed values is controlled by EA

(external access). When EA is high (internal

ROM access), the watchdog parameters are

taken from the mask programmed values. If

the watchdog is mask programmed to the

timer mode, then the autoload values and the

pre-scaler taps are taken from the SFRs.

When EA is low (external access), the

watchdog parameters are taken from the

SFRs. The user should be able to leave code

in his program which initializes the watchdog

SFRs even though he has migrated to the

mask ROM part. This allows no code

changes from EPROM prototyping to ROM

coded production parts.

1998 May 01

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