Axiom DEMO9S12XDT512, User Manual

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D E M O 9 S 1 2 X D T 5 1 2 J U L Y 1 8 , 2 0 0 8
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CAN Communications
The DEMO9S12XDT512 provides a PCA82C250 high-speed CAN physical layer interface
(PHY). A 3-pin connector provides connectivity to the off-board CAN bus. The CAN PHY
connects to the CAN0 channel on the MCU. The PHY supports data rates up to 1 MBps with
edge-rate control to reduce EMI/RFI. The figure below shows the pin-out of the CAN_PORT
connector.
Figure 9. CAN_PORT Connector
1 CAN_H
2 GND
3 CAN_L
The CAN PHY connects to the CAN0
channel in the MCU
MODE
The MODE option header allows the MCU to be configured between the various modes of op-
eration. Refer to the MC9S12XDP512 Device User Guide for further details on operational
modes. Although no external memory is available on the DEMO9S12XDT512 board, external
bus signals are available at expansion headers J1 and J2. The figure below shows the set-
tings for the MODE option header. MODE selection status is latched at the rising edge of RE-
SET. An internal pull-down biases the MODA and MODB signals during boot. After RESET,
the MODA and MODB signals revert to general-purpose I/O functionality.
The MODE option header is not installed in default configuration. Internal bias configures the
MCU for single-chip operation out of reset. To configure the MCU for expanded mode opera-
tion, install a 2x2 pin header and install shunts as noted below.
Figure 10. MODE Option Header
Installed Removed
4 3 MODB MODB = 1 MODB = 0
2 1 MODA MODA = 1 MODA = 0
MODE
NOTE : MODE selection pin status is latched on the rising edge of RESET
NOTE : This header is not installed in default configuration
VRH/VRL
MCU inputs VRH and VRL provide the upper and lower voltage reference for the analog to
digital (ATD) converter. By default, VRH is tied to VDD and VRL is tied to ground. Adequate
filtering has been added to provide a voltage reference with minimal ripple. Either, or both,
references may be isolated to provide alternate ATD input references. A test point via on each
signal, labeled VRH, or VRL, provides a convenient attach point.