83C576 Datasheet, PDF(9/46 Page) NXP Semiconductors – 80C51 8-bit microcontroller family 8K/256 OTP/ROM, 6 channel 10-bit A/D, 4 comparators, failure detect circuitry, watchdog timer

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83C576 Datasheet, PDF (9/46 Pages) NXP Semiconductors – 80C51 8-bit microcontroller family 8K/256 OTP/ROM, 6 channel 10-bit A/D, 4 comparators, failure detect circuitry, watchdog timer

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Philips Semiconductors

80C51 8-bit microcontroller family

8K/256 OTP/ROM, 6 channel 10-bit A/D, 4 comparators,

failure detect circuitry, watchdog timer

Product specification

83C576/87C576

Table 1.

SYMBOL

87C576 Special Function Registers (Continued)

DESCRIPTION

DIRECT

BIT ADDRESS, SYMBOL, OR ALTERNATIVE PORT FUNCTION

ADDRESS MSB

LSB

TH0

TH1

TH2#

TL0

TL1

TL2#

Timer High 0

Timer High 1

Timer High 2

Timer Low 0

Timer Low 1

Timer Low 2

8CH

8DH

CDH

8AH

8BH

CCH

RESET

VALUE

00H

TMOD

UCS#

Timer Mode

UPI Control/Status

89H GATE C/T

GATE C/T

M0 00H

86H

ST7

ST6

ST5

ST4

IBF OBE/OBF 00H

WDCON# Watchdog Timer Control

C4H PRE2

WDL#

Watchdog Timer Reload

WFEED1# Watchdog Feed 1

C1H

C2H

WFEED2# Watchdog Feed 2

C3H

* SFRs are bit addressable.

# SFRs are modified from or added to the 80C51 SFRs.

1. Reset value depends on reset source.

PRE1

PRE0 LVRE OFRE

DPD

WDRUN

WDMOD

11111111B

00H

xxH

The 8XC576 has a number of failure detect circuits to prevent

abnormal operating conditions. these failure detect circuits generate

resets as shown in Figure 1.

POWER ON CLEAR / POWER ON FLAG

An on-chip Power On Detect Circuit resets the 8XC576 and sets the

Power Off Flag (PCON.4) on power up or if VCC drops to zero

momentarily. The POF can only be cleared by software. The RST

pin is not driven by the power on detect circuit. The POF can be

read by software to determine that a power failure has occurred and

can also be set by software.

LOW VOLTAGE DETECT

An on-chip Low Voltage Detect circuit sets the Low Voltage Flag

(PCON.3) if VCC drops below VLOW (see DC Electrical

Characteristics) and resets the 8XC576 if the Low Voltage Reset

Enable bit (WDCON.4) is set. If the LVRE is cleared, the reset is

disabled but LVF will still be set if VCC is low. The RST pin is not

driven by the low voltage detect circuit. The LVF can be read by

software to determine that VCC was low. The LVF can be set or

cleared by software.

OSCILLATOR FAIL DETECT

An on-chip Oscillator Fail Detect circuit sets the Oscillator Fail Flag

(PCON.5) if the oscillator frequency drops below OSCF for one or

more cycles (see AC Electrical Characteristics: OSCF) and resets

the 8XC576 if the Oscillator Fail Reset Enable bit (WDCON.3) is set.

If OFRE is cleared, the reset is disabled but OSF will still be set if

the oscillator fails. The RST pin is not driven by the oscillator fail

detect circuit. The OSF can be read by software to determine that

an oscillator failure has occurred. The OSF can be set or cleared by

software.

LOW ACTIVE RESET

One of the most notable features on this part is the low active reset.

The low active reset operates exactly the same as high active reset

with the exception that the part is put into the reset mode by

applying a low level to the reset pin. For power-on reset it is also

necessary to invert the power-on reset circuit; connecting the 8.2K

resistor from the reset pin to VCC and the 10Âµf capacitor from the

reset pin to ground. Figure 1 shows the reset related circuitry.

When reset the port pins on the 8XC576 are driven high

synchronously.

The 8XC576 also has Low voltage detection circuitry that will, if

enabled, force the part to reset when VCC (on the part) fails below a

set level. Low Voltage Reset is enabled by a normal reset. Low

Voltage Reset can be disabled by clearing LVRE (bit 4 in the

WDCON SFR) then executing a watchdog feed sequence (A5H to

WFEED1 followed immediately by 5AH to WFEED2). In addition

there is a flag (LVF) that is set if a low voltage condition is detected.

The LVF flag is set even if the Low Voltage detection circuitry is

disabled. Notice that the Low voltage detection circuitry does not

drive the RST# pin so the LVF flag is the only way that the

microcontroller can determine if it has been reset due to a low

voltage condition.

The 8XC576 has an on-chip power-on detection circuit that sets the

POF (PCON.4) flag on power up or if the VCC level momentarily

drops to 0V. This flag can be used to determine if the part is being

started from a power-on (cold start) or if a reset has occurred due to

another condition (warm start).

The 8XC576 can be reset in software by setting the RST bit of the

AUXR register (AUXR.3). See Figure 1 for reset diagram.

1998 Jun 04

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