P87C54SBAA,512 NXP Semiconductors, P87C54SBAA,512 Datasheet - Page 31

• Manufacturer Part Number: P87C54SBAA,512
• Description: IC 80C51 MCU 16K OTP 44-PLCC
• Manufacturer: NXP Semiconductors
• Series: 87Cr

Specifications of P87C54SBAA,512

• Core Processor: 8051
• Core Size: 8-Bit
• Speed: 16MHz
• Connectivity: EBI/EMI, UART/USART
• Peripherals: POR
• Number Of I /o: 32
• Program Memory Size: 16KB (16K x 8)
• Program Memory Type: OTP
• Ram Size: 256 x 8
• Voltage - Supply (vcc/vdd): 2.7 V ~ 5.5 V
• Oscillator Type: Internal
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 44-PLCC
• Processor Series: P87C5x
• Core: 80C51
• Data Bus Width: 8 bit
• Data Ram Size: 256 B
• Interface Type: UART
• Maximum Clock Frequency: 16 MHz
• Number Of Programmable I/os: 32
• Number Of Timers: 3
• Operating Supply Voltage: 2.7 V to 5.5 V
• Maximum Operating Temperature: + 70 C
• Mounting Style: SMD/SMT
• 3rd Party Development Tools: PK51, CA51, A51, ULINK2
• Minimum Operating Temperature: 0 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Eeprom Size: -
• Data Converters: -
• Lead Free Status / Rohs Status: Details
• Other names: 568-1252-5; 935258650512; P87C54SBAA

Philips Semiconductors
(8XC51FX and 8XC51RX+ ONLY)
PCA Watchdog Timer
An on-board watchdog timer is available with the PCA to improve
the reliability of the system without increasing chip count. Watchdog
timers are useful for systems that are susceptible to noise, power
glitches, or electrostatic discharge. Module 4 is the only PCA
module that can be programmed as a watchdog. However, this
module can still be used for other modes if the watchdog is not
needed.
Figure 25 shows a diagram of how the watchdog works. The user
pre-loads a 16-bit value in the compare registers. Just like the other
compare modes, this 16-bit value is compared to the PCA timer
value. If a match is allowed to occur, an internal reset will be
generated. This will not cause the RST pin to be driven high.
In order to hold off the reset, the user has three options:
1. periodically change the compare value so it will never match the
2. periodically change the PCA timer value so it will never match
3. disable the watchdog by clearing the WDTE bit before a match
2000 Aug 07
80C51 8-bit microcontroller family
8K–64K/256–1K OTP/ROM/ROMless, low voltage (2.7V–5.5V),
low power, high speed (33MHz)
PCA timer,
the compare values, or
occurs and then re-enable it.
WRITE TO
CCAP4L
0
WRITE TO
CCAP4H
1
RESET
ENABLE
Figure 25. PCA Watchdog Timer m(Module 4 only)
CCAP4H
16–BIT COMPARATOR
CH
PCA TIMER/COUNTER
CIDL
––
ECOMn
WDTE
CCAP4L
CL
CAPPn
31
––
0
MODULE 4
MATCH
The first two options are more reliable because the watchdog timer
is never disabled as in option #3. If the program counter ever goes
astray, a match will eventually occur and cause an internal reset.
The second option is also not recommended if other PCA modules
are being used. Remember, the PCA timer is the time base for all
modules; changing the time base for other modules would not be a
good idea. Thus, in most applications the first solution is the best
option.
Figure 26 shows the code for initializing the watchdog timer.
Module 4 can be configured in either compare mode, and the WDTE
bit in CMOD must also be set. The user’s software then must
periodically change (CCAP4H,CCAP4L) to keep a match from
occurring with the PCA timer (CH,CL). This code is given in the
WATCHDOG routine in Figure 26.
This routine should not be part of an interrupt service routine,
because if the program counter goes astray and gets stuck in an
infinite loop, interrupts will still be serviced and the watchdog will
keep getting reset. Thus, the purpose of the watchdog would be
defeated. Instead, call this subroutine from the main program within
2
16
CAPNn
count of the PCA timer.
––
0
MATn
––
1
8XC51RA+/RB+/RC+/RD+/80C51RA+
TOGn
CPS1
X
CPS0
PWMn
8XC51FA/FB/FC/80C51FA
0
ECCFn
ECF
X
Product specification
CMOD
(D9H)
RESET
CCAPM4
(DEH)
SU00832
8XC54/58