M37544G2AGP#U0 Renesas Electronics America, M37544G2AGP#U0 Datasheet - Page 56

• Manufacturer Part Number: M37544G2AGP#U0
• Description: IC 740 MCU OTP 8K 32LQFP
• Manufacturer: Renesas Electronics America
• Series: 740/38000r

Specifications of M37544G2AGP#U0

• Core Processor: 740
• Core Size: 8-Bit
• Speed: 8MHz
• Connectivity: SIO, UART/USART
• Peripherals: WDT
• Number Of I /o: 25
• Program Memory Size: 8KB (8K x 8)
• Program Memory Type: QzROM
• Ram Size: 256 x 8
• Voltage - Supply (vcc/vdd): 4 V ~ 5.5 V
• Data Converters: A/D 6x8b
• Oscillator Type: Internal
• Operating Temperature: -20°C ~ 85°C
• Package / Case: 32-LQFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Eeprom Size: -

REJ03B0108-0103
page 54 of 72
7544 Group (QzROM version)
5. Setup for I/O ports
Setup I/O ports using hardware and software as follows:
<Hardware>
• Connect a resistor of 100 Ω or more to an I/O port in series.
<Software>
• As for an input port, read data several times by a program for
• As for an output port, since the output data may reverse because
• Rewrite data to direction registers and pull-up control registers at
Fig. 62 Setup for I/O ports
6. Providing of watchdog timer function by software
If a microcomputer runs away because of noise or others, it can
be detected by a software watchdog timer and the microcomputer
can be reset to normal operation. This is equal to or more effective
than program runaway detection by a hardware watchdog timer.
The following shows an example of a watchdog timer provided by
software.
In the following example, to reset a microcomputer to normal op-
eration, the main routine detects errors of the interrupt processing
routine and the interrupt processing routine detects errors of the
main routine.
This example assumes that interrupt processing is repeated mul-
tiple times in a single main routine processing.
checking whether input levels are equal or not.
of noise, rewrite data to its port latch at fixed periods.
fixed periods.
Data bus
Direction register
Port latch
Rev.1.03
Mar 31, 2009
I/O port
pins
O.K.
N.G.
Noise
Noise
<The main routine>
• Assigns a single byte of RAM to a software watchdog timer
• Watches the operation of the interrupt processing routine by
• Detects that the interrupt processing routine has failed and de-
<The interrupt processing routine>
• Decrements the SWDT contents by 1 at each interrupt process-
• Determines that the main routine operates normally when the
• Detects that the main routine has failed and determines to
Fig. 63 Watchdog timer by software
(SWDT) and writes the initial value N in the SWDT once at each
execution of the main routine. The initial value N should satisfy
the following condition:
N+1 ≥ (Counts of interrupt processing executed in each main
routine)
As the main routine execution cycle may change because of an
interrupt processing or others, the initial value N should have a
margin.
comparing the SWDT contents with counts of interrupt process-
ing after the initial value N has been set.
termines to branch to the program initialization routine for
recovery processing in the following case:
If the SWDT contents do not change after interrupt processing.
ing.
SWDT contents are reset to the initial value N at almost fixed
cycles (at the fixed interrupt processing count).
branch to the program initialization routine for recovery process-
ing in the following case:
If the SWDT contents are not initialized to the initial value N but
continued to decrement and if they reach 0 or less.
≠N
Interrupt processing
Main processing
routine errors
Main routine
(SWDT)← N
(SWDT)
=N?
CLI
N
Interrupt processing routine
(SWDT) ← (SWDT)—1
Interrupt processing
Main routine
(SWDT)
errors
≤0?
≤0
Return
RTI
>0