PIC24HJ64 Datasheet

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PIC24HJ32GP302/304, <strong>PIC24HJ64</strong>GPX02/X04, AND PIC24HJ128GPX02/X04 FIGURE 18-1: ECAN MODULE BLOCK DIAGRAM DMA Controller TRB7 Tx/Rx Buffer Control Register TRB6 Tx/Rx Buffer Control Register TRB5 Tx/Rx Buffer Control Register TRB4 Tx/Rx Buffer Control Register TRB3 Tx/Rx Buffer Control Register TRB2 Tx/Rx Buffer Control Register TRB1 Tx/Rx Buffer Control Register TRB0 Tx/Rx Buffer Control Register RxF15 Filter RxF14 Filter RxF13 Filter RxF12 Filter RxF11 Filter RxF10 Filter RxF9 Filter RxF8 Filter RxF7 Filter RxF6 Filter RxF5 Filter RxF4 Filter RxF3 Filter RxF2 Filter RxF1 Filter RxF0 Filter RxM2 Mask RxM1 Mask RxM0 Mask Transmit Byte Sequencer Message Assembly Buffer CAN Protocol Engine Control Configuration Logic CPU Bus Interrupts C1Tx C1Rx DS70293B-page 188 Preliminary © 2008 Microchip Technology Inc.
PIC24HJ32GP302/304, <strong>PIC24HJ64</strong>GPX02/X04, AND PIC24HJ128GPX02/X04 18.3 Modes of Operation The ECAN module can operate in one of several operation modes selected by the user. These modes include: • Initialization mode • Disable mode • Normal Operation mode • Listen Only mode • Listen All Messages mode • Loopback mode Modes are requested by setting the REQOP bits (CiCTRL1). Entry into a mode is Acknowledged by monitoring the OPMODE bits (CiCTRL1). The module does not change the mode and the OPMODE bits until a change in mode is acceptable, generally during bus Idle time, which is defined as at least 11 consecutive recessive bits. 18.3.1 INITIALIZATION MODE In the Initialization mode, the module does not transmit or receive. The error counters are cleared and the interrupt flags remain unchanged. The user application has access to Configuration registers that are access restricted in other modes. The module protects the user from accidentally violating the CAN protocol through programming errors. All registers which control the configuration of the module can not be modified while the module is on-line. The ECAN module is not allowed to enter the Configuration mode while a transmission is taking place. The Configuration mode serves as a lock to protect the following registers: • All Module Control registers • Baud Rate and Interrupt Configuration registers • Bus Timing registers • Identifier Acceptance Filter registers • Identifier Acceptance Mask registers 18.3.2 DISABLE MODE In Disable mode, the module does not transmit or receive. The module has the ability to set the WAKIF bit due to bus activity, however, any pending interrupts remains and the error counters retains their value. If the REQOP bits (CiCTRL1) = 001, the module enters the Module Disable mode. If the module is active, the module waits for 11 recessive bits on the CAN bus, detect that condition as an Idle bus, then accept the module disable command. When the OPMODE bits (CiCTRL1) = 001, that indicates whether the module successfully went into Module Disable mode. The I/O pins reverts to normal I/O function when the module is in the Module Disable mode. The module can be programmed to apply a low-pass filter function to the CiRX input line while the module or the CPU is in Sleep mode. The WAKFIL bit (CiCFG2) enables or disables the filter. Note: Typically, if the ECAN module is allowed to transmit in a particular mode of operation and a transmission is requested immediately after the ECAN module has been placed in that mode of operation, the module waits for 11 consecutive recessive bits on the bus before starting transmission. If the user switches to Disable mode within this 11-bit period, then this transmission is aborted and the corresponding TXABT bit is set and TXREQ bit is cleared. 18.3.3 NORMAL OPERATION MODE Normal Operation mode is selected when REQOP = 000. In this mode, the module is activated and the I/O pins assumes the CAN bus functions. The module transmits and receive CAN bus messages via the CiTX and CiRX pins. 18.3.4 LISTEN ONLY MODE If the Listen Only mode is activated, the module on the CAN bus is passive. The transmitter buffers revert to the port I/O function. The receive pins remain inputs. For the receiver, no error flags or Acknowledge signals are sent. The error counters are deactivated in this state. The Listen Only mode can be used for detecting the baud rate on the CAN bus. To use this, it is necessary that there are at least two further nodes that communicate with each other. 18.3.5 LISTEN ALL MESSAGES MODE The module can be set to ignore all errors and receive any message. The Listen All Messages mode is activated by setting REQOP = ‘111’. In this mode, the data which is in the message assembly buffer, until the time an error occurred, is copied in the receive buffer and can be read via the CPU interface. 18.3.6 LOOPBACK MODE If the Loopback mode is activated, the module connects the internal transmit signal to the internal receive signal at the module boundary. The transmit and receive pins revert to their port I/O function. © 2008 Microchip Technology Inc. Preliminary DS70293B-page 189
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PIC24HJ64 Datasheet

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