FPGA
MEN Mikro Elektronik GmbH
84
20A014-00 E2 – 2007-08-16
The bidirectional power fail port can be used for two different functions. If it is used
as an output, a heartbeat LED can be driven with the value of the control register bit
HB
. If it is used as an input, the port checks the level of the power fail signal to
detect a loss of the power supply. To switch between input and output, a 16-bit
counter controls an output-enable signal. The counter value
0x1
switches the port to
an input, all other values force the port to act as an output.
The reset controller contains a system watchdog which has to be triggered by the
CPU through alternating write operations (
0xAA
and
0x55
) in configurable time
intervals. If the time interval exceeds without a correct write operation, the
watchdog executes a system reset by forcing
HRSTN
to 0. Additionally bit
WDEX
is
set in the
Reset Cause Register
to provide the reset cause information after system
restart.