ZAMC4100 datasheet(36/156 Pages) RENESAS

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ZAMC4100 Datasheet

January 26, 2016

Figure 3.3 ZAMC4100 Reset Sources

POR

WDT

sys_rst

SLEEP

mcu_rst

STBY

PWRT

tPWRT

SBC clock

OVT

DRIVERS

RSTN

SBC

RSTN

MCU

RSTN

WDTMCUF

PORF

OVTIF

WDTSYSF

Power-on-Reset (POR)

This global system reset is generated when the supply at the VDDE pin crosses the voltage thresholds specified

in Table 1.5.

WDT Reset

There are two types of watchdog timer resets: the MCU reset and the global system reset. In the event of an

abnormal condition in which the MCU fails to periodically clear the WDT counter, the WDT will attempt to reset the

MCU. However after a configurable number of consecutive MCU resets, the WDT will invoke a global system

reset where both the SBC and MCU will be re-initialized.

OVT Drivers Control Reset

The over-temperature (OVT) reset is generated if the SBC chip temperature reaches the value specified by the

parameter OVTTH (125ºC; see Table 1.5). If an OVT reset occurs, it clears all drivers’ control registers. From a

functional point of view, the OVT reset is equivalent to a shut-down signal for the drivers. It is implemented in a

way that ensures that the drivers shut down even if the system clock is not present.

The driver control registers that are reset by an OVT reset event are HBDCTRL (Table 3.13), HBDDIAG (Table

3.17), HSDCTRL (Table 3.20), and ECMCTRL (Table 3.27). The OVT reset does not influence the MCU or the

other SBC registers. If an OVT event has taken place, it is indicated in interrupt flag OVTIF of register RSTSTAT

(see Table 3.1), and if interrupt by OVT is enabled (bit OVTIE = 1), the IRQN line is forced low.

In order to recover from an OVT event (i.e., to enable the drivers again), the MCU software should first clear

interrupt flag OVTIF and then write the driver control registers again. As soon as the OVT event is active, the

driver control registers are kept in reset; i.e., the drivers cannot be enabled. In order to ensure that the OVT event

has been resolved, the MCU should try to clear OVTIF and re-check the flag. Successfully clearing OVTIF means

that the chip has cooled-down to a temperature below 125°C; i.e., it will be possible to re-enable the drivers. As

an additional step before re-enabling the drivers, it is recommended that the MCU measures the internal chip

temperature (using the ADC). This avoids enabling the drivers when the SBC temperature is close to 125°C (e.g.,

120°C) and as a result, the chip goes in OVT again a short time after the drivers are enabled.

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