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TJA1020 Datasheet(PDF) 6 Page - NXP Semiconductors |
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TJA1020 Datasheet(HTML) 6 Page - NXP Semiconductors |
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6 / 22 page  2004 Jan 13 6 Philips Semiconductors Product specification LIN transceiver TJA1020 Setting pin NSLP HIGH during standby mode results in the following events: • An immediate reset of the wake-up source flag; thus releasing the possible strong pull-down at pin TXD before the actual mode change (after tgotonorm) is performed • A change into normal slope mode if the HIGH level on pin NSLP has been maintained for a certain time period (tgotonorm) while pin TXD is pulled HIGH • A change into low slope mode if the HIGH level on pin NSLP has been maintained for a certain time period (tgotonorm) while pin TXD is pulled LOW either deliberately driven by the microcontroller, or due to a failure. In the event of a short-circuit to ground or an open-wire on pin TXD, the LIN output remains recessive (fail safe) • A reset of the wake-up request signal on pin RXD if the HIGH level on pin NSLP has been maintained for a certain time period (tgotonorm). Normal slope mode In the normal slope mode the transceiver is able to transmit and receive data via the LIN bus line. The receiver detects the data stream at the LIN bus input pin and transfers it via pin RXD to the microcontroller (see Fig.1): HIGH at a recessive level and LOW at a dominant level on the bus. The receiver has a supply voltage related threshold with hysteresis and an integrated filter to suppress bus line noise. The transmit data stream of the protocol controller at the TXD input is converted by the transmitter into a bus signal with controlled slew rate and wave shaping to minimize EME. The LIN bus output pin is pulled HIGH via an internal slave termination resistor. For a master application an external resistor in series with a diode should be connected between pin INH or BAT on one side and pin LIN on the other side (see Fig.7). Being in the sleep or standby mode, the TJA1020 enters normal slope mode whenever a HIGH level on pin NSLP is maintained for a time of at least tgotonorm provided its preceding positive edge is executed while pin TXD is already set to HIGH. The TJA1020 switches to sleep mode in case of a LOW level on pin NSLP, maintained during a certain time period (tgotosleep) while pin TXD is already set to HIGH. Low slope mode The only difference between the normal slope mode and the low slope mode is the transmitter behaviour. In the low slope mode the transmitter output stage drives the LIN bus line with lengthened rise and fall slopes. This will further reduce the already outstanding EME in the normal slope mode. The low slope mode is perfectly suited for applications where transmission speed is not critical. The mode selection is done by the LIN transceiver after a positive edge on pin NSLP, maintained for a certain time period (tgotonorm). If pin TXD is LOW at that time, the low slope mode is entered, otherwise the normal mode is entered. The transition to the low slope mode will be executed during an open pin TXD (fail-safe), a short-circuit from pin TXD to ground (fail-safe) or an intended LOW level of pin TXD programmed by the microcontroller. The transmitter is enabled after a LOW-to-HIGH transition on pin TXD. In the event of a short-circuit to ground on pin TXD, the transmitter will be disabled. Wake-up There are three ways to wake-up a TJA1020 which is in sleep mode: 1. Remote wake-up via a dominant bus state 2. Local wake-up via a negative edge at pin NWAKE 3. Mode change (pin NSLP is HIGH) from sleep mode to normal slope/low slope mode. Remote and local wake-up A falling edge at pin NWAKE followed by a LOW level maintained for a certain time period (tNWAKE) results in a local wake-up. The pin NWAKE provides an internal pull-up towards pin BAT. In order to prevent EMI issues, it is recommended to connect an unused pin NWAKE to pin BAT. If, during power-up, pin NWAKE is LOW for a certain period of time (tNWAKE) this will also result in a local wake-up. A falling edge at pin LIN followed by a LOW level maintained for a certain time period (tBUS) and a rising edge at pin LIN respectively (see Fig.4) results in a remote wake-up. After a local or remote wake-up pin INH is activated (it goes HIGH) and the internal slave termination resistor is switched on. The wake-up request is indicated by a LOW active wake-up request signal on pin RXD to interrupt the microcontroller. |
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