| Part Numbert | Mfg | Packt | D/C | Descriptiont | Qty | Company/Contact |
N74AC11244D Datasheet
N74AC11244D Price Figure 6 0n page 6 shows a correct trigger sequence. The positive edge of the trigger signal starts a new monitoring cycle with the disable time, t2. To ensure correct opera- tion of the microcontroller, the watchdog needs to be triggered three times correctly before it sets its enable output. This feature is used to activate or deactivate safety-criti- cal components which have to be switched to a certain condition (emergency status) in the case of a microcontroller malfunction. As soon as there is an incorrect trigger sequence, the enable signal is reset and it takes a sequence of three correct triggers before enable is reset. N74AC11244D on stock SOFT-START CAPACITOR A soft-start capacitor is used to provide the soft-start feature. When the input voltage is first applied, or when the SD(SS) pin is allowed to go high, the soft-start capacitor is charged by a current source (approximately 2 pA). When the SD(SS) pin voltage reaches 0.6V (shutdown threshold), the internal regulator circuitry starts to operate. The current charging the soft-start capacitor increases from 2 pA to approximately 10 pA. With the SD(SS) pin voltage between 0.6V and l.3V, the level of the current limit is zero, which means the output voltage is still zero. When the SD(SS) pin voltage increases beyond l.3V, the current limit starts to increase. The switch duty cycle, which is controlled by the level of the current limit, starts with narrow pulses and gradually gets wider. At the same time, the output voltage of the converter increases towards the nominal value, which brings down the output voltage of the error amplifier. When the output of the error amplifier is less than the current limit voltage, it takes over the control of the duty cycle. The converter enters the normal current-mode PWM operation. The SD(SS) pin voltage is eventually charged up to about 2V. The soft-start time can be estimated as: Tss = CSS X 0.6V/2 IJA + CSS X (2V-0.6V)/10 }JA As a record is received by the XA-G49, the information in the record is stored internally and a checksum calculation is performed. The operation indicated by the record type is not performed until the entire record has been received. Should an error occur in the checksum, the XA-G49 will send an "X" out the serial port indicating a checksum error. If the checksum calculation is found to match the checksum in the record, then the command will be executed. In most cases, successful reception of the record will be indicated by transmitting a "." character out the serial port (displaying the contents of the internal program memory is an exception). |
