MSCAN
The APS12DT256SLK provides one PCA82C250 high-speed CAN physical interface. 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 slew-rate control.
The figure below shows the pin-out of the CAN_PORT connector.
Figure 6. CAN_PORT Connector
1
CAN_H
2
GND
3
CAN_L
The CAN PHY connects to the CAN0
channel in the MCU
Also the MCU provides support for additional CAN channels. All CAN channels supported are
routed to the connector J1 for use if needed. Consult the Device User Guide for the installed
MCU for further details.
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 an easy way to attach an alternate reference voltage.
A 0-ohm configuration resistor allows isolation of each reference voltage. Removing R10
isolates VRH while removing R12 isolates VRL. Install a suitably sized 0-ohm resistors in
these locations to restore the board to its default configuration.
Care must be exercised when using alternate input references. The associated configuration
resistor must be removed before applying an alternate voltage reference or the board may be
damaged. Also, no input protection is provided; incorrect configuration will damage the MCU.
The table below summarizes the changes necessary to use alternate VRH and/or VRL.
Table 3: ATD Reference Voltage
Installed
(Default)
Removed
R4
VRH = VDD
VRH provided by user
R5
VRL = GND
VRL provided by user
NOTE: Damage to the board may result if an alternate reference voltage is attached without
first removing the associated configuration resistor.
14 Freescale Semiconductor
