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MCZ33742EG Datasheet(PDF) 42 Page - Freescale Semiconductor, Inc |
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MCZ33742EG Datasheet(HTML) 42 Page - Freescale Semiconductor, Inc |
42 / 70 page Analog Integrated Circuit Device Data 42 Freescale Semiconductor 33742 FUNCTIONAL DEVICE OPERATION OPERATIONAL MODES Figure 23 illustrates how the wake-up signal is generated. First the CAN signal is detected by a low consumption receiver (WU receiver). Then the signal passes through a pulse width filter, which discards the undesired pulses. The pulse must have a width bigger than 0.5 μs and smaller than 500 μs to be accepted. When a pulse is discarded, the pulse counter is reset and no wake-up signal is generated. When a pulse is accepted, the pulse counter is incremented and, after three pulses, the internal wake-up signal is asserted. Each one of the pulses must be spaced by no more than 500 μs. If not, the counter will be reset and no wake-up signal will be generated. This is accomplished by the wake-up timeout generator. The wake-up cycle is completed (and the wake-up flag reset) when the CAN interface is brought to CAN Normal mode. Figure 23. Wake-Up Functional Block Diagram CAN WAKE-UP REPORT The CAN wake-up reporting depend upon the low power mode the SBC is in. If the SBC is placed into Sleep mode (VDD and V2 off), the CAN wake-up or any wake-up results in the VDD regulator turning on, leading to turning on the MCU supply and releasing reset. If the 33742 is in Stop mode (V2 off and VDD active), the CAN wake-up or any wake-up is signalled by a pulse on the INT output. In addition the CANWU bit is set in the CAN register. If the SBC is in Normal or Standby mode and the CAN interface is in Sleep mode with wake-up enabled, the CAN wake-up is reported by the CANWU bit in the CAN register. In the event the SBC is in Normal mode and CAN Sleep mode with wake-up enabled, it is recommended that the user check for the CANWU bit prior to placing the 33742 in Sleep or Stop mode in case bus traffic has occurred while the CAN interface was in Sleep mode. After a CAN wake-up, a flag is set in the CAN register. Bit CANWU reports the CAN wake-up event while the 33742 was in Sleep or Stop mode. This bit is set until the CAN is in placed by SPI command into TXRX mode and the CAN register can be read. CAN BUS DIAGNOSTIC The SBC can diagnose CANH or CANL lines short to GND, shorts to VSUP or VDD. As illustrated in Figure 24, several single-ended comparators are implemented on the CANH and CANL bus lines. These comparators monitor the bus voltage level in the recessive and dominant states. This information is then managed by a logic circuit to determine if a failure has occurred and to report it. Table 11 indicates the state of the comparators in the event of bus failure and the state of the drivers; that is, whether they are recessive or dominant. + Internal Wake-up Latch RST Time-out RST Counter Pulse OK Narrow Pulse Pulse Width Filter Time-out Generator Standby WU Receiver CANH CANL Signal |
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