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Line 395: − There are ''two'' CAN buses -- CAN1 and CAN2. CAN1 is the primary CAN bus used for the flight stack, while CAN2 is a secondary bus that exists only for possible future use. All boards should implement CAN1. The schematic for the CAN system for each board is well defined, and should be implemented exactly as shown. The CAN connector, in addition to the above described four nodes, includes a +3.3_CAN pin and a GND pin. GND should be common grounded, while +3.3_CAN should be used to power the CAN transceiver -- it should power no other device on a board, and the CAN transceiver should exclusively use this pin as its power source.+ Line 413:
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Line 449: − + − #Make sure to '''NOT IMPLEMENT''' any of the following restricted pins, unless specifically agreed upon in advance (don't touch them at all, even as an input) -- 6 (R_MCU), 22 (RX2) 112 (CAN_MODE -- this shouldn't go anywhere except your Transceiver) − #Be sure to connect pin 112 (CAN_SPD) from the data bus to the speed pin on your CAN Transceiver. Without this, it will not function. − #Make sure pin 7 (R_ALL) is directly wired to your MCU reset pin, to allow Core Avionics remote reset. − #If using RTC, make sure to implement pin 5 (+VBCKP). − − === Self-Help FAQ === − #If implementing the data bus SPI or I2C lines, this should be agreed upon by current HABEES members as an appropriate use of the Core Avionics I2C/SPI buses before action is taken. − #If using either of the dedicated Core Avionics Hardware UARTs (pins 23/24 and 25/26), this should be agreed as constituting a reasonable use -- being that it is critical enough to warrant their use, or otherwise cannot be achieved. − #If using either DAC (pins 27 and 28) verify it can only be used as an input, and will not be used in any way as an output (IE do not output to those pins). − #If using any of the Core Avionics GPIO's on the data bus (pins 29-36, 38-41), be sure that it isn't currently being used by another board (unless you specifically want it to be, such as using the pin as a feed-through signal line), whether the pin is able to perform the desired action (PWM, ADC, DIO), and agree amongst HABEES members that it is a reasonable and just usage of the pin, which would henceforth be reserved for your purpose. − #If using any of the current RESERVED pins (37, 42-111, 113-120), agree amongst HABEES members that it is a just and fair usage of the pin, which would henceforth be reserved for your purpose. − #Make sure, unless for some reason you're using it, CAN2 is not connected to anything. − #Make sure +3.3_CAN is used only to power the transceiver, and nothing else. − #Make sure CAN_SPD is hard-wired to the transceiver speed pin.
no edit summary
=== CAN BUS ===
=== CAN BUS ===
[[File:cbus.JPG | right| thumb | <center> CAN Bus Pin-Out </center>]]
[[File:cbus_rev1.JPG | right| thumb | <center> CAN Bus Pin-Out </center>]]
The CAN bus is the primary means of communication within the flight stack. The CAN bus is the means by which any board can request data from the avionics, receive data from the avionics, as well as receive commands and requests from the avionics for a specific action.
The CAN bus is the primary means of communication within the flight stack. The CAN bus is the means by which any board can request data from the avionics, receive data from the avionics, as well as receive commands and requests from the avionics for a specific action.
The required, standardized HONEY transceiver is the TI_SN65HVD230.
The required, standardized HONEY transceiver is the TI_SN65HVD230.
The schematic for the CAN system for each board is well defined, and should be implemented exactly as shown. The CAN connector, in addition to the above described four nodes, includes a +3.3_CAN pin and a GND pin. GND should be common grounded, while +3.3_CAN should be used to power the CAN transceiver -- it should power no other device on a board, and the CAN transceiver should exclusively use this pin as its power source.
Shown here is the CAN schematic that should be implemented on any board.
Shown here is the CAN schematic that should be implemented on any board.
=== CAN Terminating Jumpers ===
=== CAN Terminating Jumpers ===
The CAN Terminating Impedance Connector, a 2x4 male terminal strip, is used for the purpose of applying the necessary 120-ohm terminating impedance on each end of the CAN bus. Since the current HONEY architecture dictates that the Core Avionics and Core BMS occupy the top and bottom positions in the stack, they are currently the only boards to utilize this connector. However, as the architecture may evolve, and positions of boards change, it is necessary to implement this connector so that your board may effectively institute the necessary terminating impedance.
The CAN Terminating Impedance Connector, a 2x2 male terminal strip, is used for the purpose of applying the necessary 120-ohm terminating impedance on each end of the CAN bus. Since the current HONEY architecture dictates that the Core Avionics and Core BMS occupy the top and bottom positions in the stack, they are currently the only boards to utilize this connector.
[[File:can_stack.JPG | right| thumb | <center> CAN Stack Implementation </center>]]
[[File:can_stack.JPG | right| thumb | <center> CAN Stack Implementation </center>]]
[[File:can_wires.JPG | right| thumb | <center> CAN Feed-through </center>]]
[[File:can_wires.JPG | right| thumb | <center> CAN Feed-through </center>]]
A CAN bus requires a 120 ohm resistor between CAN HIGH and CAN LOW for the first and last devices on the bus to prevent reflections. This is achieved by jumping two pins, with a resistor in between. In this case, for CAN1, this is achieved by the top two pins in this connector. 1_TERM_1 and 1_TERM_2 are open-circuit, but, when jumped, become closed. 1_TERM_2 is connected to CAN1_L. 1_TERM_1 is connected to one end of a 120 ohm resistor -- the other end of the resistor is connected to CAN1_H. Thereby, by placing a jumper on the two pins and closing the circuit, a 120 ohm impedance is effectively engaged, properly terminating the bus. The same is true for pins 3/4, which are for CAN2 (not used by most boards). Pins 4-8 exist solely as a position to place jumpers when they are not used by a board -- IE when the board is not implementing the terminating impedance.
A CAN bus requires a 120 ohm resistor between CAN HIGH and CAN LOW for the first and last devices on the bus to prevent reflections. This is achieved by jumping two pins, with a resistor in between. In this case, for CAN1, this is achieved by the top two pins in this connector. 1_TERM_1 and 1_TERM_2 are open-circuit, but, when jumped, become closed. 1_TERM_2 is connected to CAN1_L. 1_TERM_1 is connected to one end of a 120 ohm resistor -- the other end of the resistor is connected to CAN1_H. Thereby, by placing a jumper on the two pins and closing the circuit, a 120 ohm impedance is effectively engaged, properly terminating the bus.
The schematic for the implementation of this connector, including both the relevant portion of the stack connector, and its connection to the CAN transceiver, is shown here.
The schematic for the implementation of this connector, including both the relevant portion of the stack connector, and its connection to the CAN transceiver, is shown here.
[[File:allcan.JPG | right| thumb | <center> CAN, showing terminating impedance implemented </center>]]
[[File:allcan_rev1.JPG | right| thumb | <center> CAN, showing terminating impedance implemented </center>]]
=== Required Implementation ===
=== Required Implementation ===
#Use the latest HABEES_STACK_TEMPLATE part from the Altium library. This is to be kept updated by HABEES members to reflect changes in pinout, physical layout, etc, and is required to make your board meet the physical and electrical bare requirements.
#Use the HABEES_NEW_STACK part from the Altium library. This is to be kept updated by HABEES members to reflect changes in pinout, physical layout, etc, and is required to make your board meet the physical and electrical bare requirements.
#Common Ground all GND nets on the stack connectors to your GND -- this includes two on the Power Bus, four on the Data Bus, and one on the CAN bus.
#Common Ground all GND nets on the stack connectors to your GND -- this includes two on the Power Bus, four on the Data Bus, and one on the CAN bus.
#For the nets of the power bus that your board is utilizing, make sure to electrically short the nets together, and join them by a 40/50-mil trace. The reason there are two pins is to provide a higher current-limit, so you should tie them together to ensure proper rating.
#For the nets of the power bus that your board is utilizing, make sure to electrically short the nets together, and join them by a 40/50-mil trace. The reason there are two pins is to provide a higher current-limit, so you should tie them together to ensure proper rating.
#Make '''SURE TO IMPLEMENT''' the following pins as INPUTS to your MCU -- 7 (R_ALL), 8 (S_READY), 9 (LOW_PWR), 10 (FMODE), 11-14 (System Flags 3-6, reserved), 21 (CHIRP -- should go to a Serial RX pin on your MCU).
#Make '''SURE TO IMPLEMENT''' the following pins as INPUTS to your MCU -- 7 (R_ALL), 8 (S_READY), 9 (LOW_PWR), 10 (FMODE), 11-14 (System Flags 3-6, reserved), 21 (CHIRP -- should go to a Serial RX pin on your MCU).
#Make sure to properly implement the CAN Bus -- duplicate the existing schematic for the primary circuit, and verify that you have properly implemented the terminating impedance sub-circuit.
#Make sure to properly implement the CAN Bus -- duplicate the existing schematic for the primary circuit, and verify that you have properly implemented the terminating impedance sub-circuit.
#Be sure to use +3.3_CAN pin from the CAN Bus EXCLUSIVELY to power your Transceiver, and make sure it powers nothing else.
#Be sure to use +3.3_CAN pin from the CAN Bus EXCLUSIVELY to power your Transceiver, and make sure it powers nothing else.
#Make sure no component of the board extends more than 0.25" over the board edge.
#Make sure no component of the board extends more than 0.25" over the board edge.
[[Category: High Altitude Balloons]][[Category: HABEES]][[Category: HONEY]]
[[Category: High Altitude Balloons]][[Category: HABEES]][[Category: HONEY]]