S32R274 EVB User Guide
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The reset switch SW2 can be used to reset the MCU. The reset switch signal is connect to the MCU
reset signals RESET_B (through jumper J47) and the connection can be released by lifting the according
jumper. For normal operation leave jumper J47 populated. If external control of RESET_B is required
then connection of a control signal to pin 2 of J47 can be made. Pushing the reset switch will also reset
peripherals that are connected to the board reset signal signal RST-SW.
Since the S32R274 device offers both internal and external regulation modes this is configurable on the
daughtercard, and thus an external voltage monitoring IC (U18 – Linear Devices LTC2905) is utilised to
protect the device when in external regulation mode and the device low voltage detect (LVD)
mechanism is disabled. This circuit monitors the 1.25v (core supply) and 3.3v IO supply domain and
will hold the device in reset via VREG_POR_B until these supplies are within the expected voltage
range. This circuit is active in both internal and external regulation schemes.
Figure 15.
Voltage monitoring and reset circuit
Table 9.
Reset circuit jumper settings
Jumper
Description
J47
Connect reset switch circuit to RESET_B pin
J48
Connect reset switch circuit to VREG_POR_B pin
4.3
MCU External Clock Circuit
In addition to the internal 16 MHz oscillator, the MCU can be clocked by different external sources. The
EVB system supports four possible MCU clock sources:
1.
40MHz crystal Y3 (The MCU only has a 40Mhz input)
2.
External clock input to the EVB via the SMA connector (J20), driving the MCU EXTAL signal
3.
External differential clock input to the EVB via SMA connectors (J20 & J22), driving MCU
EXTAL and XTAL with negative and positive clock signals respectively
4.
External differential or single ended clock input to the EVB via the MIPI-CSI2 connector, for
use with the Eagle MR3003 RF front end board.